[cc] Fix CompositorFrameSinkSupport BeginFrameAck interface.

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 96aff284e98f3a286dd797b8165e697b60795e1e..b2e4baec18d3d47167d539779ed6237245e93644 100644
--- a/cc/ipc/mojo_compositor_frame_sink.mojom
+++ b/cc/ipc/mojo_compositor_frame_sink.mojom
@@ -35,6 +35,10 @@ interface MojoCompositorFrameSink {
   SubmitCompositorFrame(cc.mojom.LocalSurfaceId local_surface_id,
                         cc.mojom.CompositorFrame frame);
 
+  // Notifies the frame sink that a BeginFrame was completed, but that no
+  // CompositorFrame was produced as a result of it.
+  BeginFrameDidNotSwap(cc.mojom.BeginFrameAck ack);
+
   // Notify that the surface is no longer in use (and is okay to be evicted) so
   // that its resources gets returned in time.
   EvictFrame();