diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index ca0b8e82001..124eec3dab7 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -30,7 +30,7 @@ use msg::compositor_msg::{LayerProperties, ScrollPolicy};
 use msg::constellation_msg::AnimationState;
 use msg::constellation_msg::Msg as ConstellationMsg;
 use msg::constellation_msg::{ConstellationChan, Key, KeyModifiers, KeyState, LoadData};
-use msg::constellation_msg::{NavigationDirection, PipelineId, SubpageId, WindowSizeData};
+use msg::constellation_msg::{NavigationDirection, PipelineId, WindowSizeData};
 use pipeline::CompositionPipeline;
 use png;
 use profile_traits::mem::{self, ReportKind, Reporter, ReporterRequest};
@@ -164,10 +164,6 @@ pub struct IOCompositor<Window: WindowMethods> {
     /// A data structure to cache unused NativeSurfaces.
     surface_map: SurfaceMap,
 
-    /// Information about subpage layers that are pending. The keys in this map are the
-    /// pipeline/subpage IDs of the parent.
-    pending_subpage_layers: HashMap<(PipelineId, SubpageId), PendingSubpageLayerInfo>,
-
     /// Pipeline IDs of subpages that the compositor has seen in a layer tree but which have not
     /// yet been painted.
     pending_subpages: HashSet<PipelineId>,
@@ -315,7 +311,6 @@ impl<Window: WindowMethods> IOCompositor<Window> {
             has_seen_quit_event: false,
             ready_to_save_state: ReadyState::Unknown,
             surface_map: SurfaceMap::new(BUFFER_MAP_SIZE),
-            pending_subpage_layers: HashMap::new(),
             pending_subpages: HashSet::new(),
         }
     }
@@ -517,15 +512,6 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                 self.window.head_parsed();
             }
 
-            (Msg::CreateLayerForSubpage(parent_pipeline_id,
-                                        parent_subpage_id,
-                                        subpage_pipeline_id),
-             ShutdownState::NotShuttingDown) => {
-                 self.create_layer_for_subpage(parent_pipeline_id,
-                                               parent_subpage_id,
-                                               subpage_pipeline_id);
-            }
-
             (Msg::CollectMemoryReports(reports_chan), ShutdownState::NotShuttingDown) => {
                 let mut reports = vec![];
                 let name = "compositor-task";
@@ -546,11 +532,6 @@ impl<Window: WindowMethods> IOCompositor<Window> {
 
             (Msg::PipelineExited(pipeline_id), _) => {
                 self.pending_subpages.remove(&pipeline_id);
-
-                // FIXME(pcwalton): This is a total hack. But it'll get complicated to do this
-                // properly, since we need to get rid of the pending subpage layers if either the
-                // parent or the child layer goes away.
-                self.pending_subpage_layers.clear();
             }
 
             // When we are shutting_down, we need to avoid performing operations
@@ -713,9 +694,7 @@ impl<Window: WindowMethods> IOCompositor<Window> {
         root_layer.collect_old_layers(self, pipeline_id, new_layers, &mut pipelines_removed);
 
         for pipeline_removed in pipelines_removed.into_iter() {
-            self.pending_subpage_layers.remove(&(pipeline_removed.parent_pipeline_id,
-                                                 pipeline_removed.parent_subpage_id));
-            self.pending_subpages.remove(&pipeline_removed.child_pipeline_id);
+            self.pending_subpages.remove(&pipeline_removed);
         }
     }
 
@@ -829,52 +808,21 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                     scrolls_overflow_area: true,
                 };
 
-                // We need to map from the (pipeline ID, subpage ID) pair to the pipeline ID of
-                // the subpage itself. The constellation is the source of truth for that
-                // information, so go ask it. In the meantime, store the information in the list of
-                // pending subpage layers.
-                self.pending_subpage_layers.insert((pipeline_id, subpage_layer_info.subpage_id),
-                                                   PendingSubpageLayerInfo {
-                    subpage_layer_properties: subpage_layer_properties,
-                    container_layer_id: layer_properties.id,
-                });
-                self.constellation_chan.0.send(ConstellationMsg::PrepareForSubpageLayerCreation(
-                        pipeline_id,
-                        subpage_layer_info.subpage_id)).unwrap();
-            }
-
-            parent_layer.add_child(new_layer.clone());
-        }
-    }
-
-    fn create_layer_for_subpage(&mut self,
-                                parent_pipeline_id: PipelineId,
-                                parent_subpage_id: SubpageId,
-                                subpage_pipeline_id: Option<PipelineId>) {
-        let subpage_pipeline_id = match subpage_pipeline_id {
-            Some(subpage_pipeline_id) => subpage_pipeline_id,
-            None => return,
-        };
-        if let Some(PendingSubpageLayerInfo {
-            subpage_layer_properties,
-            container_layer_id
-        }) = self.pending_subpage_layers.remove(&(parent_pipeline_id, parent_subpage_id)) {
-            if let Some(container_layer) =
-                    self.find_layer_with_pipeline_and_layer_id(parent_pipeline_id,
-                                                               container_layer_id) {
                 let wants_scroll_events = if subpage_layer_properties.scrolls_overflow_area {
                     WantsScrollEventsFlag::WantsScrollEvents
                 } else {
                     WantsScrollEventsFlag::DoesntWantScrollEvents
                 };
-                let subpage_layer = CompositorData::new_layer(subpage_pipeline_id,
+                let subpage_layer = CompositorData::new_layer(subpage_layer_info.pipeline_id,
                                                               subpage_layer_properties,
                                                               wants_scroll_events,
-                                                              container_layer.tile_size);
+                                                              new_layer.tile_size);
                 *subpage_layer.masks_to_bounds.borrow_mut() = true;
-                container_layer.add_child(subpage_layer);
-                self.pending_subpages.insert(subpage_pipeline_id);
+                new_layer.add_child(subpage_layer);
+                self.pending_subpages.insert(subpage_layer_info.pipeline_id);
             }
+
+            parent_layer.add_child(new_layer.clone());
         }
     }
 
@@ -901,7 +849,6 @@ impl<Window: WindowMethods> IOCompositor<Window> {
 
         let ConstellationChan(ref chan) = self.constellation_chan;
         chan.send(ConstellationMsg::FrameSize(subpage_layer_info.pipeline_id,
-                                              subpage_layer_info.subpage_id,
                                               layer_properties.rect.size)).unwrap();
     }
 
@@ -1495,7 +1442,7 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                 }
 
                 // Check if there are any pending frames. If so, the image is not stable yet.
-                if self.pending_subpage_layers.len() > 0 || self.pending_subpages.len() > 0 {
+                if self.pending_subpages.len() > 0 {
                     return false
                 }
 
@@ -1914,16 +1861,3 @@ pub enum CompositingReason {
     /// The window has been zoomed.
     Zoom,
 }
-
-struct PendingSubpageLayerInfo {
-    subpage_layer_properties: LayerProperties,
-    container_layer_id: LayerId,
-}
-
-#[derive(Copy, Clone)]
-pub struct RemovedPipelineInfo {
-    pub parent_pipeline_id: PipelineId,
-    pub parent_subpage_id: SubpageId,
-    pub child_pipeline_id: PipelineId,
-}
-
diff --git a/components/compositing/compositor_layer.rs b/components/compositing/compositor_layer.rs
index 261802c9a81..d2fb73e7b10 100644
--- a/components/compositing/compositor_layer.rs
+++ b/components/compositing/compositor_layer.rs
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use azure::azure_hl;
-use compositor::{IOCompositor, RemovedPipelineInfo};
+use compositor::IOCompositor;
 use euclid::length::Length;
 use euclid::point::{Point2D, TypedPoint2D};
 use euclid::rect::Rect;
@@ -12,7 +12,7 @@ use layers::color::Color;
 use layers::geometry::LayerPixel;
 use layers::layers::{Layer, LayerBufferSet};
 use msg::compositor_msg::{Epoch, LayerId, LayerProperties, ScrollPolicy};
-use msg::constellation_msg::{PipelineId, SubpageId};
+use msg::constellation_msg::{PipelineId};
 use script_traits::CompositorEvent::{ClickEvent, MouseDownEvent, MouseMoveEvent, MouseUpEvent};
 use script_traits::ConstellationControlMsg;
 use std::rc::Rc;
@@ -43,8 +43,8 @@ pub struct CompositorData {
     /// to track their current scroll position even while their content_offset does not change.
     pub scroll_offset: TypedPoint2D<LayerPixel, f32>,
 
-    /// The pipeline ID and subpage ID of this layer, if it represents a subpage.
-    pub subpage_info: Option<(PipelineId, SubpageId)>,
+    /// The pipeline ID of this layer, if it represents a subpage.
+    pub subpage_info: Option<PipelineId>,
 }
 
 impl CompositorData {
@@ -62,7 +62,7 @@ impl CompositorData {
             painted_epoch: Epoch(0),
             scroll_offset: Point2D::typed(0., 0.),
             subpage_info: layer_properties.subpage_layer_info.map(|subpage_layer_info| {
-                (subpage_layer_info.pipeline_id, subpage_layer_info.subpage_id)
+                subpage_layer_info.pipeline_id
             }),
         };
 
@@ -156,7 +156,7 @@ pub trait RcCompositorLayer {
                                   compositor: &mut IOCompositor<Window>,
                                   pipeline_id: PipelineId,
                                   new_layers: &[LayerProperties],
-                                  pipelines_removed: &mut Vec<RemovedPipelineInfo>)
+                                  pipelines_removed: &mut Vec<PipelineId>)
                                   where Window: WindowMethods;
 }
 
@@ -427,7 +427,7 @@ impl RcCompositorLayer for Rc<Layer<CompositorData>> {
                                   compositor: &mut IOCompositor<Window>,
                                   pipeline_id: PipelineId,
                                   new_layers: &[LayerProperties],
-                                  pipelines_removed: &mut Vec<RemovedPipelineInfo>)
+                                  pipelines_removed: &mut Vec<PipelineId>)
                                   where Window: WindowMethods {
         fn find_root_layer_for_pipeline(layer: &Rc<Layer<CompositorData>>, pipeline_id: PipelineId)
                                         -> Option<Rc<Layer<CompositorData>>> {
@@ -449,7 +449,7 @@ impl RcCompositorLayer for Rc<Layer<CompositorData>> {
                 compositor: &mut IOCompositor<Window>,
                 pipeline_id: PipelineId,
                 new_layers: &[LayerProperties],
-                pipelines_removed: &mut Vec<RemovedPipelineInfo>)
+                pipelines_removed: &mut Vec<PipelineId>)
                 where Window: WindowMethods {
             // Traverse children first so that layers are removed
             // bottom up - allowing each layer being removed to properly
@@ -475,23 +475,17 @@ impl RcCompositorLayer for Rc<Layer<CompositorData>> {
                     return new_layers.iter().any(|properties| properties.id == extra_data.id);
                 }
 
-                if let Some(ref subpage_info_for_this_layer) = extra_data.subpage_info {
+                if let Some(layer_pipeline_id) = extra_data.subpage_info {
                     for layer_properties in new_layers.iter() {
                         // Keep this layer if a reference to it exists.
                         if let Some(ref subpage_layer_info) = layer_properties.subpage_layer_info {
-                            if subpage_layer_info.pipeline_id == subpage_info_for_this_layer.0 &&
-                                    subpage_layer_info.subpage_id ==
-                                    subpage_info_for_this_layer.1 {
+                            if subpage_layer_info.pipeline_id == layer_pipeline_id {
                                 return true
                             }
                         }
                     }
 
-                    pipelines_removed.push(RemovedPipelineInfo {
-                        parent_pipeline_id: subpage_info_for_this_layer.0,
-                        parent_subpage_id: subpage_info_for_this_layer.1,
-                        child_pipeline_id: extra_data.pipeline_id,
-                    });
+                    pipelines_removed.push(extra_data.pipeline_id);
                 }
 
                 // When removing a layer, clear any tiles and surfaces associated with the layer.
diff --git a/components/compositing/compositor_task.rs b/components/compositing/compositor_task.rs
index f74813cdf33..2b3b572a011 100644
--- a/components/compositing/compositor_task.rs
+++ b/components/compositing/compositor_task.rs
@@ -12,7 +12,7 @@ use layers::layers::{BufferRequest, LayerBufferSet};
 use layers::platform::surface::{NativeDisplay, NativeSurface};
 use msg::compositor_msg::{Epoch, FrameTreeId, LayerId, LayerProperties};
 use msg::compositor_msg::{PaintListener, ScriptToCompositorMsg};
-use msg::constellation_msg::{AnimationState, ConstellationChan, PipelineId, SubpageId};
+use msg::constellation_msg::{AnimationState, ConstellationChan, PipelineId};
 use msg::constellation_msg::{Key, KeyModifiers, KeyState};
 use png;
 use profile_traits::mem;
@@ -219,10 +219,6 @@ pub enum Msg {
     ResizeTo(Size2D<u32>),
     /// A pipeline was shut down.
     PipelineExited(PipelineId),
-    /// The layer for a subpage should be created. The first two IDs are the IDs of the *parent*
-    /// pipeline and subpage, respectively, while the last ID is the pipeline ID of the subpage
-    /// itself (or `None` if it has shut down).
-    CreateLayerForSubpage(PipelineId, SubpageId, Option<PipelineId>),
 }
 
 impl Debug for Msg {
@@ -257,7 +253,6 @@ impl Debug for Msg {
             Msg::MoveTo(..) => write!(f, "MoveTo"),
             Msg::ResizeTo(..) => write!(f, "ResizeTo"),
             Msg::PipelineExited(..) => write!(f, "PipelineExited"),
-            Msg::CreateLayerForSubpage(..) => write!(f, "CreateLayerForSubpage"),
         }
     }
 }
diff --git a/components/compositing/constellation.rs b/components/compositing/constellation.rs
index 8fe576855ee..0da135022d4 100644
--- a/components/compositing/constellation.rs
+++ b/components/compositing/constellation.rs
@@ -408,9 +408,9 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
             }
             // The compositor discovered the size of a subframe. This needs to be reflected by all
             // frame trees in the navigation context containing the subframe.
-            ConstellationMsg::FrameSize(pipeline_id, subpage_id, size) => {
+            ConstellationMsg::FrameSize(pipeline_id, size) => {
                 debug!("constellation got frame size message");
-                self.handle_frame_size_msg(pipeline_id, subpage_id, &Size2D::from_untyped(&size));
+                self.handle_frame_size_msg(pipeline_id, &Size2D::from_untyped(&size));
             }
             ConstellationMsg::ScriptLoadedURLInIFrame(load_info) => {
                 debug!("constellation got iframe URL load message {:?} {:?} {:?}",
@@ -541,12 +541,6 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 debug!("constellation got NodeStatus message");
                 self.compositor_proxy.send(CompositorMsg::Status(message));
             }
-            ConstellationMsg::PrepareForSubpageLayerCreation(pipeline_id, subpage_id) => {
-                self.compositor_proxy.send(CompositorMsg::CreateLayerForSubpage(
-                        pipeline_id,
-                        subpage_id,
-                        self.subpage_map.get(&(pipeline_id, subpage_id)).map(|x| *x)))
-            }
         }
         true
     }
@@ -617,23 +611,20 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
     }
 
     fn handle_frame_size_msg(&mut self,
-                             containing_pipeline_id: PipelineId,
-                             subpage_id: SubpageId,
+                             pipeline_id: PipelineId,
                              size: &TypedSize2D<PagePx, f32>) {
         // Store the new rect inside the pipeline
-        let (pipeline_id, script_chan) = {
+        let script_chan = {
             // Find the pipeline that corresponds to this rectangle. It's possible that this
             // pipeline may have already exited before we process this message, so just
             // early exit if that occurs.
-            let pipeline_id = self.subpage_map
-                                  .get(&(containing_pipeline_id, subpage_id))
-                                  .map(|id| *id);
-            let pipeline = match pipeline_id {
-                Some(pipeline_id) => self.mut_pipeline(pipeline_id),
+            match self.pipelines.get_mut(&pipeline_id) {
+                Some(pipeline) => {
+                    pipeline.size = Some(*size);
+                    pipeline.script_chan.clone()
+                }
                 None => return,
-            };
-            pipeline.size = Some(*size);
-            (pipeline.id, pipeline.script_chan.clone())
+            }
         };
 
         script_chan.send(ConstellationControlMsg::Resize(pipeline_id, WindowSizeData {
diff --git a/components/compositing/headless.rs b/components/compositing/headless.rs
index 3a0ab67ea21..41bcc3811d2 100644
--- a/components/compositing/headless.rs
+++ b/components/compositing/headless.rs
@@ -124,7 +124,6 @@ impl CompositorEventListener for NullCompositor {
             Msg::ReturnUnusedNativeSurfaces(..) => {}
             Msg::CollectMemoryReports(..) => {}
             Msg::PipelineExited(..) => {}
-            Msg::CreateLayerForSubpage(..) => {}
         }
         true
     }
diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
index c4937791140..4dbafd017fb 100644
--- a/components/layout/display_list_builder.rs
+++ b/components/layout/display_list_builder.rs
@@ -1289,7 +1289,6 @@ impl FragmentDisplayListBuilding for Fragment {
                 let border_padding = self.border_padding.to_physical(self.style().writing_mode);
                 Some(SubpageLayerInfo {
                     pipeline_id: iframe_fragment_info.pipeline_id,
-                    subpage_id: iframe_fragment_info.subpage_id,
                     origin: Point2D::new(border_padding.left, border_padding.top),
                 })
             }
diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 63fec117a8c..06a26863cff 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -24,7 +24,7 @@ use ipc_channel::ipc::IpcSender;
 use layout_debug;
 use model::{self, IntrinsicISizes, IntrinsicISizesContribution, MaybeAuto, specified};
 use msg::compositor_msg::{LayerId, LayerType};
-use msg::constellation_msg::{PipelineId, SubpageId};
+use msg::constellation_msg::PipelineId;
 use net_traits::image::base::Image;
 use net_traits::image_cache_task::UsePlaceholder;
 use rustc_serialize::{Encodable, Encoder};
@@ -578,17 +578,14 @@ impl ReplacedImageFragmentInfo {
 pub struct IframeFragmentInfo {
     /// The pipeline ID of this iframe.
     pub pipeline_id: PipelineId,
-    /// The subpage ID of this iframe.
-    pub subpage_id: SubpageId,
 }
 
 impl IframeFragmentInfo {
     /// Creates the information specific to an iframe fragment.
     pub fn new(node: &ThreadSafeLayoutNode) -> IframeFragmentInfo {
-        let (pipeline_id, subpage_id) = node.iframe_pipeline_and_subpage_ids();
+        let pipeline_id = node.iframe_pipeline_id();
         IframeFragmentInfo {
             pipeline_id: pipeline_id,
-            subpage_id: subpage_id,
         }
     }
 
diff --git a/components/layout/wrapper.rs b/components/layout/wrapper.rs
index 91ba3f958a8..74fdc869759 100644
--- a/components/layout/wrapper.rs
+++ b/components/layout/wrapper.rs
@@ -37,7 +37,7 @@ use gfx::display_list::OpaqueNode;
 use gfx::text::glyph::CharIndex;
 use incremental::RestyleDamage;
 use ipc_channel::ipc::IpcSender;
-use msg::constellation_msg::{PipelineId, SubpageId};
+use msg::constellation_msg::PipelineId;
 use opaque_node::OpaqueNodeMethods;
 use script::dom::attr::AttrValue;
 use script::dom::bindings::codegen::InheritTypes::{CharacterDataCast, ElementCast};
@@ -1011,14 +1011,13 @@ impl<'ln> ThreadSafeLayoutNode<'ln> {
         }
     }
 
-    /// If this node is an iframe element, returns its pipeline and subpage IDs. If this node is
+    /// If this node is an iframe element, returns its pipeline ID. If this node is
     /// not an iframe element, fails.
-    pub fn iframe_pipeline_and_subpage_ids(&self) -> (PipelineId, SubpageId) {
+    pub fn iframe_pipeline_id(&self) -> PipelineId {
         unsafe {
             let iframe_element = HTMLIFrameElementCast::to_layout_js(self.get_jsmanaged())
                 .expect("not an iframe element!");
-            ((*iframe_element.unsafe_get()).containing_page_pipeline_id().unwrap(),
-             (*iframe_element.unsafe_get()).subpage_id().unwrap())
+            (*iframe_element.unsafe_get()).pipeline_id().unwrap()
         }
     }
 }
diff --git a/components/msg/compositor_msg.rs b/components/msg/compositor_msg.rs
index 681f5161f2c..8c411148c9a 100644
--- a/components/msg/compositor_msg.rs
+++ b/components/msg/compositor_msg.rs
@@ -4,7 +4,7 @@
 
 use app_units::Au;
 use azure::azure_hl::Color;
-use constellation_msg::{Key, KeyModifiers, KeyState, PipelineId, SubpageId};
+use constellation_msg::{Key, KeyModifiers, KeyState, PipelineId};
 use euclid::{Matrix4, Point2D, Rect, Size2D};
 use ipc_channel::ipc::IpcSender;
 use layers::layers::{BufferRequest, LayerBufferSet};
@@ -169,8 +169,6 @@ pub enum ScriptToCompositorMsg {
 pub struct SubpageLayerInfo {
     /// The ID of the pipeline.
     pub pipeline_id: PipelineId,
-    /// The ID of the subpage.
-    pub subpage_id: SubpageId,
     /// The offset of the subpage within this layer (to account for borders).
     pub origin: Point2D<Au>,
 }
diff --git a/components/msg/constellation_msg.rs b/components/msg/constellation_msg.rs
index cefcd0da4c8..0cbcd352722 100644
--- a/components/msg/constellation_msg.rs
+++ b/components/msg/constellation_msg.rs
@@ -239,7 +239,7 @@ pub enum Msg {
     LoadComplete(PipelineId),
     /// Dispatched after the DOM load event has fired on a document
     DOMLoad(PipelineId),
-    FrameSize(PipelineId, SubpageId, Size2D<f32>),
+    FrameSize(PipelineId, Size2D<f32>),
     LoadUrl(PipelineId, LoadData),
     ScriptLoadedURLInIFrame(IframeLoadInfo),
     Navigate(Option<(PipelineId, SubpageId)>, NavigationDirection),
@@ -291,9 +291,6 @@ pub enum Msg {
                          IpcSender<Result<(IpcSender<CanvasMsg>, usize), String>>),
     /// Status message to be displayed in the chrome, eg. a link URL on mouseover.
     NodeStatus(Option<String>),
-    /// Requests that the pipeline ID of the subpage identified by a (pipeline ID, subpage ID)
-    /// pair be sent to the compositor via a `CreateLayerForSubpage` message.
-    PrepareForSubpageLayerCreation(PipelineId, SubpageId),
 }
 
 #[derive(Clone, Eq, PartialEq, Deserialize, Serialize, Debug)]
@@ -463,12 +460,12 @@ thread_local!(pub static PIPELINE_NAMESPACE: Cell<Option<PipelineNamespace>> = C
 pub struct PipelineNamespaceId(pub u32);
 
 #[derive(Clone, PartialEq, Eq, Copy, Hash, Debug, Deserialize, Serialize, HeapSizeOf)]
-pub struct PipelineIndex(u32);
+pub struct PipelineIndex(pub u32);
 
 #[derive(Clone, PartialEq, Eq, Copy, Hash, Debug, Deserialize, Serialize, HeapSizeOf)]
 pub struct PipelineId {
-    namespace_id: PipelineNamespaceId,
-    index: PipelineIndex
+    pub namespace_id: PipelineNamespaceId,
+    pub index: PipelineIndex
 }
 
 impl PipelineId {
diff --git a/components/script/dom/htmliframeelement.rs b/components/script/dom/htmliframeelement.rs
index 115dd139854..b8df7d9fd78 100644
--- a/components/script/dom/htmliframeelement.rs
+++ b/components/script/dom/htmliframeelement.rs
@@ -222,6 +222,11 @@ impl HTMLIFrameElement {
     pub fn subpage_id(&self) -> Option<SubpageId> {
         self.subpage_id.get()
     }
+
+    #[inline]
+    pub fn pipeline_id(&self) -> Option<PipelineId> {
+        self.pipeline_id.get()
+    }
 }
 
 pub fn Navigate(iframe: &HTMLIFrameElement, direction: NavigationDirection) -> Fallible<()> {