Don't schedule an animation during compositing dirty-bit setting unless needed.

Source/core/rendering/compositing/RenderLayerCompositor.h

Index: Source/core/rendering/compositing/RenderLayerCompositor.h
diff --git a/Source/core/rendering/compositing/RenderLayerCompositor.h b/Source/core/rendering/compositing/RenderLayerCompositor.h
index 00cfd63742939aa73617181c57be9840e8aa9e48..1973235c18aefb92a7b5b1b586dc96ab0ab8ce3d 100644
--- a/Source/core/rendering/compositing/RenderLayerCompositor.h
+++ b/Source/core/rendering/compositing/RenderLayerCompositor.h
@@ -199,6 +199,8 @@ public:
 
     virtual String debugName(const GraphicsLayer*) OVERRIDE;
 
+    void scheduleAnimationIfNeeded();
+
 private:
     class OverlapMap;
 
@@ -233,6 +235,8 @@ private:
         RenderLayer* clippingAncestorForMostRecentMapping;
     };
 
+    bool hasUnresolvedDirtyBits();
+
     bool canSquashIntoCurrentSquashingOwner(const RenderLayer* candidate, const SquashingState&, const RenderLayer* clippingAncestor);
 
     CompositingStateTransitionType computeCompositedLayerUpdate(RenderLayer*);