Mac ÜC: Enable back-pressure for the browser compositor

cc/output/output_surface.h

Index: cc/output/output_surface.h
diff --git a/cc/output/output_surface.h b/cc/output/output_surface.h
index f992e9788c5b393e8a694dc40d6951873579bd56..98a48304b8b1fa0c85c700cd7c4a5d38d4de335e 100644
--- a/cc/output/output_surface.h
+++ b/cc/output/output_surface.h
@@ -125,6 +125,7 @@ class CC_EXPORT OutputSurface {
   // passed in (though it will not take ownership of the CompositorFrame
   // itself).
   virtual void SwapBuffers(CompositorFrame* frame);
+  virtual void OnSwapBuffersComplete();
 
   // Notifies frame-rate smoothness preference. If true, all non-critical
   // processing should be stopped, or lowered in priority.
@@ -182,8 +183,6 @@ class CC_EXPORT OutputSurface {
   void SetMemoryPolicy(const ManagedMemoryPolicy& policy);
   void UpdateAndMeasureGpuLatency();
 
-  void OnSwapBuffersComplete();
-
   bool external_stencil_test_enabled_;
 
   base::WeakPtrFactory<OutputSurface> weak_ptr_factory_;