Update from chromium https://crrev.com/304586

cc/surfaces/surface_aggregator.h

Index: cc/surfaces/surface_aggregator.h
diff --git a/cc/surfaces/surface_aggregator.h b/cc/surfaces/surface_aggregator.h
index 31d35ddc7f4e67e1cfbcec2c1fcb090b30b71243..aeeb59013998b4606ab1f4e1c58180272a7fa742 100644
--- a/cc/surfaces/surface_aggregator.h
+++ b/cc/surfaces/surface_aggregator.h
@@ -52,6 +52,10 @@ class CC_SURFACES_EXPORT SurfaceAggregator {
                        SurfaceId surface_id);
   void CopyPasses(const DelegatedFrameData* frame_data, Surface* surface);
 
+  // Remove Surfaces that were referenced before but aren't currently
+  // referenced from the ResourceProvider.
+  void RemoveUnreferencedChildren();
+
   bool TakeResources(Surface* surface,
                      const DelegatedFrameData* frame_data,
                      RenderPassList* render_pass_list);