Bug 1347758 - part2 : remove add/removeMediaContent() and related codes. r=Ehsan

Since the window would know when need to resume the media, we don't need the
add/removeMediaContent() anymore.

MozReview-Commit-ID: F9MSiqqnOiV

dom/html/HTMLMediaElement.cpp

@@ -4309,7 +4309,6 @@ nsresult HTMLMediaElement::BindToTree(nsIDocument* aDocument, nsIContent* aParen
     // The preload action depends on the value of the autoplay attribute.
     // It's value may have changed, so update it.
     UpdatePreloadAction();
-    aDocument->AddMediaContent(this);
   }
 
   NotifyDecoderActivityChanges();
@@ -4542,9 +4541,6 @@ void HTMLMediaElement::UnbindFromTree(bool aDeep,
 {
   mUnboundFromTree = true;
   mVisibilityState = Visibility::UNTRACKED;
-  if (OwnerDoc()) {
-    OwnerDoc()->RemoveMediaContent(this);
-  }
 
   nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);