Bug 880094 - Provide a stable state for HTMLTrackElement asynchronous functions. r=cpearce

- Removed HTMLMediaElement::AsyncAwaitStableState and exposed a new method,
HTMLMediaElement::RunInStableState, that allows any nsIRunnable to run on
the app shell and take advantage of IsCancelled() code in an nsMediaEvent.
- HTMLTrackElement now uses this to call HTMLTrackElement::LoadResource.
- Changed test_texttrackcue.html to listen for MediaElement's "loadedmetadata"
to ensure that we wait until the cues are loaded before testing and set
preload=auto to get it to pass on Android.

content/html/content/public/HTMLMediaElement.h

@@ -321,6 +321,13 @@ public:
    */
   void SetRequestHeaders(nsIHttpChannel* aChannel);
 
+  /**
+   * Asynchronously awaits a stable state, whereupon aRunnable runs on the main
+   * thread. This adds an event which run aRunnable to the appshell's list of
+   * sections synchronous the next time control returns to the event loop.
+   */
+  void RunInStableState(nsIRunnable* aRunnable);
+
   /**
    * Fires a timeupdate event. If aPeriodic is true, the event will only
    * be fired if we've not fired a timeupdate event (for any reason) in the

content/html/content/src/HTMLMediaElement.cpp

@@ -667,12 +667,12 @@ typedef void (HTMLMediaElement::*SyncSectionFn)();
 class nsSyncSection : public nsMediaEvent
 {
 private:
-  SyncSectionFn mClosure;
+  nsCOMPtr<nsIRunnable> mRunnable;
 public:
   nsSyncSection(HTMLMediaElement* aElement,
-                SyncSectionFn aClosure) :
+                nsIRunnable* aRunnable) :
     nsMediaEvent(aElement),
-    mClosure(aClosure)
+    mRunnable(aRunnable)
   {
   }
 
@@ -680,20 +680,16 @@ public:
     // Silently cancel if our load has been cancelled.
     if (IsCancelled())
       return NS_OK;
-    (mElement.get()->*mClosure)();
+    mRunnable->Run();
     return NS_OK;
   }
 };
 
 static NS_DEFINE_CID(kAppShellCID, NS_APPSHELL_CID);
 
-// Asynchronously awaits a stable state, whereupon aClosure runs on the main
-// thread. This adds an event which run aClosure to the appshell's list of
-// sections synchronous the next time control returns to the event loop.
-void AsyncAwaitStableState(HTMLMediaElement* aElement,
-                           SyncSectionFn aClosure)
+void HTMLMediaElement::RunInStableState(nsIRunnable* aRunnable)
 {
-  nsCOMPtr<nsIRunnable> event = new nsSyncSection(aElement, aClosure);
+  nsCOMPtr<nsIRunnable> event = new nsSyncSection(this, aRunnable);
   nsCOMPtr<nsIAppShell> appShell = do_GetService(kAppShellCID);
   appShell->RunInStableState(event);
 }
@@ -702,7 +698,8 @@ void HTMLMediaElement::QueueLoadFromSourceTask()
 {
   ChangeDelayLoadStatus(true);
   mNetworkState = nsIDOMHTMLMediaElement::NETWORK_LOADING;
-  AsyncAwaitStableState(this, &HTMLMediaElement::LoadFromSourceChildren);
+  RunInStableState(
+    NS_NewRunnableMethod(this, &HTMLMediaElement::LoadFromSourceChildren));
 }
 
 void HTMLMediaElement::QueueSelectResourceTask()
@@ -712,7 +709,8 @@ void HTMLMediaElement::QueueSelectResourceTask()
     return;
   mHaveQueuedSelectResource = true;
   mNetworkState = nsIDOMHTMLMediaElement::NETWORK_NO_SOURCE;
-  AsyncAwaitStableState(this, &HTMLMediaElement::SelectResourceWrapper);
+  RunInStableState(
+    NS_NewRunnableMethod(this, &HTMLMediaElement::SelectResourceWrapper));
 }
 
 /* void load (); */

content/html/content/src/HTMLTrackElement.cpp

@@ -304,7 +304,7 @@ HTMLTrackElement::BindToTree(nsIDocument* aDocument,
     media->NotifyAddedSource();
     LOG(PR_LOG_DEBUG, ("Track element sent notification to parent."));
 
-    nsContentUtils::AddScriptRunner(
+    mMediaParent->RunInStableState(
       NS_NewRunnableMethod(this, &HTMLTrackElement::LoadResource));
   }
 

content/media/test/test_texttrackcue.html

@@ -21,13 +21,13 @@ SpecialPowers.pushPrefEnv({"set": [["media.webvtt.enabled", true]]},
   function() {
     var video = document.createElement("video");
     video.src = "seek.webm";
+    video.preload = "auto";
     var trackElement = document.createElement("track");
     trackElement.src = "basic.vtt";
     trackElement.kind = "subtitles";
     document.getElementById("content").appendChild(video);
     video.appendChild(trackElement);
-    run_tests();
-    function run_tests() {
+    video.addEventListener("loadedmetadata", function run_tests() {
       // Re-que run_tests() at the end of the event loop until the track
       // element has loaded its data.
       if (trackElement.readyState == 1) {
@@ -116,7 +116,7 @@ SpecialPowers.pushPrefEnv({"set": [["media.webvtt.enabled", true]]},
       todo_is(cueList.length, 4, "Cue list length should be 4.");
 
       SimpleTest.finish();
-    }
+    });
   }
 );