Remove DisplayListTraversal

It's no longer necessary because we always just walk through the
display list one item at a time.

components/gfx/display_list/mod.rs

@@ -61,8 +61,7 @@ impl DisplayList {
 
     // Returns the text index within a node for the point of interest.
     pub fn text_index(&self, node: OpaqueNode, point_in_item: &Point2D<Au>) -> Option<usize> {
-        let mut traversal = DisplayListTraversal::new(self);
+        for item in &self.list {
-        while let Some(item) = traversal.next() {
             match item {
                 &DisplayItem::Text(ref text) => {
                     let base = item.base();
@@ -96,94 +95,6 @@ impl DisplayList {
     }
 }
 
-pub struct DisplayListTraversal<'a> {
-    pub display_list: &'a DisplayList,
-    pub next_item_index: usize,
-    pub first_item_index: usize,
-    pub last_item_index: usize,
-}
-
-impl<'a> DisplayListTraversal<'a> {
-    pub fn new(display_list: &'a DisplayList) -> DisplayListTraversal {
-        DisplayListTraversal {
-            display_list: display_list,
-            next_item_index: 0,
-            first_item_index: 0,
-            last_item_index: display_list.list.len(),
-        }
-    }
-
-    pub fn new_partial(display_list: &'a DisplayList,
-                       stacking_context_id: StackingContextId,
-                       start: usize,
-                       end: usize)
-                       -> DisplayListTraversal {
-        debug_assert!(start <= end);
-        debug_assert!(display_list.list.len() > start);
-        debug_assert!(display_list.list.len() > end);
-
-        let stacking_context_start = display_list.list[0..start].iter().rposition(|item|
-            match item {
-                &DisplayItem::PushStackingContext(ref item) =>
-                    item.stacking_context.id == stacking_context_id,
-                _ => false,
-            }).unwrap_or(start);
-        debug_assert!(stacking_context_start <= start);
-
-        DisplayListTraversal {
-            display_list: display_list,
-            next_item_index: stacking_context_start,
-            first_item_index: start,
-            last_item_index: end + 1,
-        }
-    }
-
-    pub fn previous_item_id(&self) -> usize {
-        self.next_item_index - 1
-    }
-
-    pub fn skip_to_end_of_stacking_context(&mut self, id: StackingContextId) {
-        self.next_item_index = self.display_list.list[self.next_item_index..].iter()
-                                                                             .position(|item| {
-            match item {
-                &DisplayItem::PopStackingContext(ref item) => item.stacking_context_id == id,
-                _ => false
-            }
-        }).unwrap_or(self.display_list.list.len());
-        debug_assert!(self.next_item_index < self.last_item_index);
-    }
-}
-
-impl<'a> Iterator for DisplayListTraversal<'a> {
-    type Item = &'a DisplayItem;
-
-    fn next(&mut self) -> Option<&'a DisplayItem> {
-        while self.next_item_index < self.last_item_index {
-            debug_assert!(self.next_item_index <= self.last_item_index);
-
-            let reached_first_item = self.next_item_index >= self.first_item_index;
-            let item = &self.display_list.list[self.next_item_index];
-
-            self.next_item_index += 1;
-
-            if reached_first_item {
-                return Some(item)
-            }
-
-            // Before we reach the starting item, we only emit stacking context boundaries. This
-            // is to ensure that we properly position items when we are processing a display list
-            // slice that is relative to a certain stacking context.
-            match item {
-                &DisplayItem::PushStackingContext(_) |
-                &DisplayItem::PopStackingContext(_) => return Some(item),
-                _ => {}
-            }
-        }
-
-        None
-    }
-}
-
 /// Display list sections that make up a stacking context. Each section  here refers
 /// to the steps in CSS 2.1 Appendix E.
 ///

components/layout/webrender_helpers.rs

@@ -10,8 +10,7 @@
 use app_units::Au;
 use euclid::{Point2D, Vector2D, Rect, SideOffsets2D, Size2D};
 use gfx::display_list::{BorderDetails, BorderRadii, BoxShadowClipMode, ClipScrollNodeType};
-use gfx::display_list::{ClippingRegion, DisplayItem, DisplayList, DisplayListTraversal};
+use gfx::display_list::{ClippingRegion, DisplayItem, DisplayList, StackingContextType};
-use gfx::display_list::StackingContextType;
 use msg::constellation_msg::PipelineId;
 use style::computed_values::{image_rendering, mix_blend_mode, transform_style};
 use style::values::computed::{BorderStyle, Filter};
@@ -222,7 +221,6 @@ impl ToTransformStyle for transform_style::T {
 
 impl WebRenderDisplayListConverter for DisplayList {
     fn convert_to_webrender(&self, pipeline_id: PipelineId) -> DisplayListBuilder {
-        let traversal = DisplayListTraversal::new(self);
         let mut builder = DisplayListBuilder::with_capacity(pipeline_id.to_webrender(),
                                                             self.bounds().size.to_sizef(),
                                                             1024 * 1024); // 1 MB of space
@@ -230,7 +228,7 @@ impl WebRenderDisplayListConverter for DisplayList {
         let mut current_clip_and_scroll_info = pipeline_id.root_clip_and_scroll_info();
         builder.push_clip_and_scroll_info(current_clip_and_scroll_info);
 
-        for item in traversal {
+        for item in &self.list {
             item.convert_to_webrender(&mut builder, &mut current_clip_and_scroll_info);
         }
         builder