[cc] Pass on BeginFrameAcks from CompositorEBFS through RWHVAura, DFH.

cc/ipc/compositor_frame_metadata_struct_traits.h

Index: cc/ipc/compositor_frame_metadata_struct_traits.h
diff --git a/cc/ipc/compositor_frame_metadata_struct_traits.h b/cc/ipc/compositor_frame_metadata_struct_traits.h
index c58ba45b4b2cdbf6ee0d2f966cf8b3c7ca80a069..49e10aca9aad5914ada0c9c388e8c978140bd987 100644
--- a/cc/ipc/compositor_frame_metadata_struct_traits.h
+++ b/cc/ipc/compositor_frame_metadata_struct_traits.h
@@ -116,6 +116,11 @@ struct StructTraits<cc::mojom::CompositorFrameMetadataDataView,
     return metadata.content_source_id;
   }
 
+  static cc::BeginFrameAck begin_frame_ack(

[dcheng, 2017/03/17 05:54:02]

Return a const reference here--even though it's a POD, it's still not free to
copy

[Eric Seckler, 2017/03/17 11:06:44]

Done.

+      const cc::CompositorFrameMetadata& metadata) {
+    return metadata.begin_frame_ack;
+  }
+
   static bool Read(cc::mojom::CompositorFrameMetadataDataView data,
                    cc::CompositorFrameMetadata* out);
 };