Bug 1550633 - part1 : HTMLTrackElement should not load resource when its text track is disable. r=jya

According to the spec step2 [1], we should not load resource for the track element which text track is disabled.

[1] https://html.spec.whatwg.org/multipage/media.html#start-the-track-processing-model

Differential Revision: https://phabricator.services.mozilla.com/D31371

--HG--
extra : moz-landing-system : lando

dom/html/HTMLTrackElement.cpp

@@ -232,10 +232,31 @@ void HTMLTrackElement::SetSrc(const nsAString& aSrc, ErrorResult& aError) {
     mChannel = nullptr;
   }
 
-  DispatchLoadResource();
+  MaybeDispatchLoadResource();
 }
 
-void HTMLTrackElement::DispatchLoadResource() {
+// This function will run partial steps from `start-the-track-processing-model`
+// and finish the rest of steps in `LoadResource()` during the stable state.
+// https://html.spec.whatwg.org/multipage/media.html#start-the-track-processing-model
+void HTMLTrackElement::MaybeDispatchLoadResource() {
+  MOZ_ASSERT(mTrack, "Should have already created text track!");
+
+  // step2, if the text track's text track mode is not set to one of hidden or
+  // showing, then return.
+  if (mTrack->Mode() == TextTrackMode::Disabled) {
+    LOG(LogLevel::Info, ("%p Do not load resource for disable track", this));
+    return;
+  }
+
+  // step3, if the text track's track element does not have a media element as a
+  // parent, return.
+  if (!mMediaParent) {
+    LOG(LogLevel::Info,
+        ("%p Do not load resource for track without media element", this));
+    return;
+  }
+
+  // step5, await a stable state and run the rest of steps.
   if (!mLoadResourceDispatched) {
     RefPtr<WebVTTListener> listener = new WebVTTListener(this);
     RefPtr<Runnable> r = NewRunnableMethod<RefPtr<WebVTTListener>>(
@@ -361,7 +382,7 @@ nsresult HTMLTrackElement::BindToTree(Document* aDocument, nsIContent* aParent,
     if (!mTrack) {
       CreateTextTrack();
     }
-    DispatchLoadResource();
+    MaybeDispatchLoadResource();
   }
 
   return NS_OK;

dom/html/HTMLTrackElement.h

@@ -94,6 +94,9 @@ class HTMLTrackElement final : public nsGenericHTMLElement {
 
   void NotifyShutdown();
 
+  // Only load resource for the non-disabled track with media parent.
+  void MaybeDispatchLoadResource();
+
  protected:
   virtual ~HTMLTrackElement();
 
@@ -113,7 +116,6 @@ class HTMLTrackElement final : public nsGenericHTMLElement {
   void CreateTextTrack();
 
  private:
-  void DispatchLoadResource();
   // Open a new channel to the HTMLTrackElement's src attribute and call
   // mListener's LoadResource().
   void LoadResource(RefPtr<WebVTTListener>&& aWebVTTListener);