Only queue a ContentClient buffer state if it has operations (bug 1427089, r=dvander)

--HG--
extra : rebase_source : 200e59db7a140b0981b1d07ebf6d8ee241336322

gfx/layers/PaintThread.h

@@ -116,6 +116,11 @@ public:
    */
   bool PrepareBuffer();
 
+  bool HasOperations() const
+  {
+    return mBufferFinalize || mBufferUnrotate || mBufferInitialize;
+  }
+
   template<typename F>
   void ForEachTextureClient(F aClosure) const
   {

gfx/layers/client/ClientPaintedLayer.cpp

@@ -228,7 +228,7 @@ ClientPaintedLayer::PaintOffMainThread()
   uint32_t flags = GetPaintFlags();
   PaintState state = mContentClient->BeginPaint(this, flags | ContentClient::PAINT_ASYNC);
 
-  if (state.mBufferState) {
+  if (state.mBufferState && state.mBufferState->HasOperations()) {
     PaintThread::Get()->PrepareBuffer(state.mBufferState);
     asyncPaints.Queue();
   }