Bug 1434804 - Pause autoplayed media if they become audible. r=kamidphish

Our autoplay blocking is trivial to defeat; just mute or volume=0 a video,
play(), and then unmute, and then you're playing audibly.

So this patch makes us pause() media that become audible atfter playback
has started.

MozReview-Commit-ID: 2RAtbohMGJO

--HG--
extra : rebase_source : 021510102374185debc89610bc6027206a0af6fc

dom/html/HTMLMediaElement.cpp

@@ -2971,6 +2971,10 @@ HTMLMediaElement::SetVolume(double aVolume, ErrorResult& aRv)
   SetVolumeInternal();
 
   DispatchAsyncEvent(NS_LITERAL_STRING("volumechange"));
+
+  // We allow inaudible autoplay. But changing our volume may make this
+  // media audible. So pause if we are no longer supposed to be autoplaying.
+  PauseIfShouldNotBePlaying();
 }
 
 void
@@ -3019,6 +3023,18 @@ HTMLMediaElement::SetMutedInternal(uint32_t aMuted)
   SetVolumeInternal();
 }
 
+void
+HTMLMediaElement::PauseIfShouldNotBePlaying()
+{
+  if (GetPaused()) {
+    return;
+  }
+  if (!AutoplayPolicy::IsMediaElementAllowedToPlay(WrapNotNull(this))) {
+    ErrorResult rv;
+    Pause(rv);
+  }
+}
+
 void
 HTMLMediaElement::SetVolumeInternal()
 {
@@ -3051,6 +3067,10 @@ HTMLMediaElement::SetMuted(bool aMuted)
   }
 
   DispatchAsyncEvent(NS_LITERAL_STRING("volumechange"));
+
+  // We allow inaudible autoplay. But changing our mute status may make this
+  // media audible. So pause if we are no longer supposed to be autoplaying.
+  PauseIfShouldNotBePlaying();
 }
 
 class HTMLMediaElement::StreamCaptureTrackSource :

dom/html/HTMLMediaElement.h

@@ -1368,6 +1368,8 @@ protected:
   void SetCDMProxyFailure(const MediaResult& aResult);
   void ResetSetMediaKeysTempVariables();
 
+  void PauseIfShouldNotBePlaying();
+
   // The current decoder. Load() has been called on this decoder.
   // At most one of mDecoder and mSrcStream can be non-null.
   RefPtr<MediaDecoder> mDecoder;