Make non-initial about:blank loads asynchronous

Don't update iframe pipeline until load completes

To preserve the previous functionality of delaying load events when a
new navigation is triggered, pending pipeline id represents the
current pending load. The load event is only fired if the load message's
pipeline id matches the pending pipeline id.

Track frame size on Frame instead of Pipeline

Disabled matchMedia test

Track creator pipeline id

components/script_traits/lib.rs

@@ -134,6 +134,8 @@ pub enum LayoutControlMsg {
 pub struct LoadData {
     /// The URL.
     pub url: ServoUrl,
+    /// The creator pipeline id if this is an about:blank load.
+    pub creator_pipeline_id: Option<PipelineId>,
     /// The method.
     #[serde(deserialize_with = "::hyper_serde::deserialize",
             serialize_with = "::hyper_serde::serialize")]
@@ -152,9 +154,14 @@ pub struct LoadData {
 
 impl LoadData {
     /// Create a new `LoadData` object.
-    pub fn new(url: ServoUrl, referrer_policy: Option<ReferrerPolicy>, referrer_url: Option<ServoUrl>) -> LoadData {
+    pub fn new(url: ServoUrl,
+               creator_pipeline_id: Option<PipelineId>,
+               referrer_policy: Option<ReferrerPolicy>,
+               referrer_url: Option<ServoUrl>)
+               -> LoadData {
         LoadData {
             url: url,
+            creator_pipeline_id: creator_pipeline_id,
             method: Method::Get,
             headers: Headers::new(),
             data: None,
@@ -211,6 +218,15 @@ pub enum DocumentActivity {
     FullyActive,
 }
 
+/// The reason why the pipeline id of an iframe is being updated.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, HeapSizeOf, Debug, Deserialize, Serialize)]
+pub enum UpdatePipelineIdReason {
+    /// The pipeline id is being updated due to a navigation.
+    Navigation,
+    /// The pipeline id is being updated due to a history traversal.
+    Traversal,
+}
+
 /// Messages sent from the constellation or layout to the script thread.
 #[derive(Deserialize, Serialize)]
 pub enum ConstellationControlMsg {
@@ -249,7 +265,7 @@ pub enum ConstellationControlMsg {
     MozBrowserEvent(PipelineId, Option<FrameId>, MozBrowserEvent),
     /// Updates the current pipeline ID of a given iframe.
     /// First PipelineId is for the parent, second is the new PipelineId for the frame.
-    UpdatePipelineId(PipelineId, FrameId, PipelineId),
+    UpdatePipelineId(PipelineId, FrameId, PipelineId, UpdatePipelineIdReason),
     /// Set an iframe to be focused. Used when an element in an iframe gains focus.
     /// PipelineId is for the parent, FrameId is for the actual frame.
     FocusIFrame(PipelineId, FrameId),
@@ -274,9 +290,6 @@ pub enum ConstellationControlMsg {
     /// Cause a `storage` event to be dispatched at the appropriate window.
     /// The strings are key, old value and new value.
     DispatchStorageEvent(PipelineId, StorageType, ServoUrl, Option<String>, Option<String>, Option<String>),
-    /// Notifies a parent pipeline that one of its child frames is now active.
-    /// PipelineId is for the parent, FrameId is the child frame.
-    FramedContentChanged(PipelineId, FrameId),
     /// Report an error from a CSS parser for the given pipeline
     ReportCSSError(PipelineId, String, usize, usize, String),
     /// Reload the given page.
@@ -312,7 +325,6 @@ impl fmt::Debug for ConstellationControlMsg {
             WebFontLoaded(..) => "WebFontLoaded",
             DispatchFrameLoadEvent { .. } => "DispatchFrameLoadEvent",
             DispatchStorageEvent(..) => "DispatchStorageEvent",
-            FramedContentChanged(..) => "FramedContentChanged",
             ReportCSSError(..) => "ReportCSSError",
             Reload(..) => "Reload",
             WebVREvents(..) => "WebVREvents",