Bug 1274626 part 6 - make MDSM change video decoder dynamically; r=jwwang

MozReview-Commit-ID: LK0gt8HhnVn

--HG--
extra : transplant_source : %BB0%84%22%CB%06%03%9F%DF%8BK%97%1F%C4%A0c%C3%AE%EE5

dom/media/MediaDecoderStateMachine.cpp

@@ -1362,6 +1362,7 @@ void MediaDecoderStateMachine::VisibilityChanged()
 
   if (mVideoDecodeSuspended) {
     mVideoDecodeSuspended = false;
+    mReader->SetVideoBlankDecode(false);
 
     if (mIsReaderSuspended) {
       return;
@@ -2640,7 +2641,7 @@ bool MediaDecoderStateMachine::IsStateMachineScheduled() const
 bool MediaDecoderStateMachine::IsVideoDecodeSuspended() const
 {
   MOZ_ASSERT(OnTaskQueue());
-  return mVideoDecodeSuspended || mIsReaderSuspended;
+  return mIsReaderSuspended;
 }
 
 void
@@ -2932,6 +2933,7 @@ MediaDecoderStateMachine::OnSuspendTimerResolved()
   DECODER_LOG("OnSuspendTimerResolved");
   mVideoDecodeSuspendTimer.CompleteRequest();
   mVideoDecodeSuspended = true;
+  mReader->SetVideoBlankDecode(true);
 }
 
 void