ui: Cleanup class/struct forward declarations

cc/ipc/mojo_compositor_frame_sink.mojom

Index: cc/ipc/mojo_compositor_frame_sink.mojom
diff --git a/cc/ipc/mojo_compositor_frame_sink.mojom b/cc/ipc/mojo_compositor_frame_sink.mojom
index f75ded36f8a57d4d312df7bc5333c9865520957a..58f69d61916f7a4752e04a3dfd99b940544448bd 100644
--- a/cc/ipc/mojo_compositor_frame_sink.mojom
+++ b/cc/ipc/mojo_compositor_frame_sink.mojom
@@ -4,7 +4,9 @@
 
 module cc.mojom;
 
+import "cc/ipc/begin_frame_args.mojom";
 import "cc/ipc/compositor_frame.mojom";
+import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/returned_resource.mojom";
 
 // A MojoCompositorFrameSink is an interface for receiving CompositorFrame
@@ -38,6 +40,18 @@ interface MojoCompositorFrameSinkClient {
   // rid of it.
   DidReceiveCompositorFrameAck();
 
+  // Notification for the client to generate a CompositorFrame.
+  OnBeginFrame(BeginFrameArgs args);
+
   // Returns resources sent to SubmitCompositorFrame to be reused or freed.
   ReclaimResources(ReturnedResourceArray resources);
 };
+
+// MojoCompositorFrameSinkPrivate is used by the display compositor host to set
+// up BeginFrameSource hierarchies.  This API lives in SurfaceManager but is
+// called from here in order to ensure that hierarchy registration does not race
+// CompositorFrameSink creation.
+interface MojoCompositorFrameSinkPrivate {
+  AddChildFrameSink(FrameSinkId child_frame_sink_id);
+  RemoveChildFrameSink(FrameSinkId child_frame_sink_id);
+};