Bug 1317167 - only need to do the untrust JS checking in play(). r=jwwang

The first checking condition in the IsAllowedPlay() is used to prevent the play() operation
is called by untrusted JS when media.autoplay.enabled=false. Therefore, we don't need to check
that in CanActivateAutoplay().

MozReview-Commit-ID: 6yqoG8ISyra

dom/html/HTMLMediaElement.cpp

@@ -4986,7 +4986,7 @@ bool HTMLMediaElement::CanActivateAutoplay()
     return false;
   }
 
-  if (!IsAllowedToPlay()) {
+  if (!IsAllowedToPlayByAudioChannel()) {
     return false;
   }
 
@@ -6051,6 +6051,12 @@ HTMLMediaElement::IsAllowedToPlay()
     return false;
   }
 
+  return IsAllowedToPlayByAudioChannel();
+}
+
+bool
+HTMLMediaElement::IsAllowedToPlayByAudioChannel()
+{
   // The media element has already been paused or blocked, so it can't start
   // playback again by script or user's intend until resuming by audio channel.
   if (mAudioChannelSuspended == nsISuspendedTypes::SUSPENDED_PAUSE ||