Bug 876133. Ensure output audio volume is updated when 'volume' attribute is set on media element. r=cpearce

--HG--
extra : rebase_source : defbb7d13b70349d321006db37f005888fb6a79e

content/html/content/public/HTMLMediaElement.h

@@ -796,6 +796,11 @@ protected:
    * Mute or unmute the audio and change the value that the |muted| map.
    */
   void SetMutedInternal(uint32_t aMuted);
+  /**
+   * Update the volume of the output audio stream to match the element's
+   * current mMuted/mVolume state.
+   */
+  void SetVolumeInternal();
 
   /**
    * Suspend (if aPauseForInactiveDocument) or resume element playback and

content/html/content/src/HTMLMediaElement.cpp

@@ -1509,7 +1509,7 @@ HTMLMediaElement::SetVolume(double aVolume, ErrorResult& aRv)
   mVolume = aVolume;
 
   // Here we want just to update the volume.
-  SetMutedInternal(mMuted);
+  SetVolumeInternal();
 
   DispatchAsyncEvent(NS_LITERAL_STRING("volumechange"));
 }
@@ -1687,6 +1687,11 @@ void HTMLMediaElement::SetMutedInternal(uint32_t aMuted)
     return;
   }
 
+  SetVolumeInternal();
+}
+
+void HTMLMediaElement::SetVolumeInternal()
+{
   float effectiveVolume = mMuted ? 0.0f : float(mVolume);
 
   if (mDecoder) {