Bug 1237827 - Be sure to clear LayerComposite::mLayerComposited between each composite. r=mattwoodrow

gfx/layers/composite/ContainerLayerComposite.cpp

@@ -564,8 +564,8 @@ RenderLayers(ContainerT* aContainer,
 
     if (layerToRender->HasLayerBeenComposited()) {
       // Composer2D will compose this layer so skip GPU composition
-      // this time & reset composition flag for next composition phase
-      layerToRender->SetLayerComposited(false);
+      // this time. The flag will be reset for the next composition phase
+      // at the beginning of LayerManagerComposite::Rener().
       gfx::IntRect clearRect = layerToRender->GetClearRect();
       if (!clearRect.IsEmpty()) {
         // Clear layer's visible rect on FrameBuffer with transparent pixels

gfx/layers/composite/LayerManagerComposite.cpp

@@ -762,6 +762,21 @@ LayerManagerComposite::PopGroupForLayerEffects(RefPtr<CompositingRenderTarget> a
                         Matrix4x4());
 }
 
+// Used to clear the 'mLayerComposited' flag at the beginning of each Render().
+static void
+ClearLayerFlags(Layer* aLayer) {
+  if (!aLayer) {
+    return;
+  }
+  if (aLayer->AsLayerComposite()) {
+    aLayer->AsLayerComposite()->SetLayerComposited(false);
+  }
+  for (Layer* child = aLayer->GetFirstChild(); child;
+       child = child->GetNextSibling()) {
+    ClearLayerFlags(child);
+  }
+}
+
 void
 LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion)
 {
@@ -773,6 +788,8 @@ LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion)
     return;
   }
 
+  ClearLayerFlags(mRoot);
+
   // At this time, it doesn't really matter if these preferences change
   // during the execution of the function; we should be safe in all
   // permutations. However, may as well just get the values onces and