cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/ipc/mojo_compositor_frame_sink.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 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/local_frame_id.mojom";
@@ skipping 17 matching lines @@
   // For successful swaps, the implementation must call
   // DidReceiveCompositorFrameAck() asynchronously when the frame has been
   // processed in order to unthrottle the next frame.
   SubmitCompositorFrame(cc.mojom.LocalFrameId local_frame_id,
                         cc.mojom.CompositorFrame frame);
 
   // Notify that the surface is no longer in use (and is okay to be evicted) so
   // that its resources gets returned in time.
   EvictFrame();
 
+  // Notifies the frame sink that a BeginFrame was completed, but that no
+  // CompositorFrame was produced as a result of it.
+  BeginFrameDidNotDraw(BeginFrameAck ack);
+
   // TODO(fsamuel): ReadbackBitmap API would be useful here.
 };
 
 interface MojoCompositorFrameSinkClient {
   // Notification that the previous CompositorFrame given to
   // SubmitCompositorFrame() has been processed and that another frame
   // can be submitted. This provides backpressure from the display compositor
   // so that frames are submitted only at the rate it can handle them.
   // TODO(fsamuel): This method ought not be necessary with unified BeginFrame.
   // However, there's a fair amount of cleanup and refactoring necessary to get
@@ skipping 11 matching lines @@
 };
 
 // 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);
 };