mus: Embedder can request and observe BeginFrame for embedded client.

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/copy_output_request.mojom";
 import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/local_surface_id.mojom";
 import "cc/ipc/surface_id.mojom";
 import "cc/ipc/returned_resource.mojom";
 import "cc/ipc/surface_sequence.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
+// Allows inspecting activity on a frame sink. This is typically used by an
+// embedder to inspect frame-sink activity of the embedded client.
+interface FrameSinkObserver {
+  OnBeginFrame();
+};
+
 // A MojoCompositorFrameSink is an interface for receiving CompositorFrame
 // structs. A CompositorFrame contains the complete output meant for display.
 // Each time a client has a graphical update, and receives an OnBeginFrame, it
 // is responsible for creating a CompositorFrame to update its portion of the
 // screen.
 interface MojoCompositorFrameSink {
   // Lets the display compositor know that the client wishes to receive the next
   // BeginFrame event.
   SetNeedsBeginFrame(bool needs_begin_frame);
 
@@ skipping 39 matching lines @@
 // CopyOutputRequests.
 interface MojoCompositorFrameSinkPrivate {
   // Claims this FrameSinkId will embed |surface_id| so it should own the
   // temporary reference to |surface_id|.
   ClaimTemporaryReference(SurfaceId surface_id);
 
   // Requests that the renderer send back a copy of the surface that this
   // CompositorFrameSink submits to. The result can be in form of a bitmap
   // or a texture. See cc::CopyOutputRequest.
   RequestCopyOfSurface(cc.mojom.CopyOutputRequest request);
+
+  // Requests begin frame messages, and installs a FrameSinkObserver, which is
+  // notified when the frame-sink receives a BeginFrame. This is typically used
+  // by an embedder to inspect frame-sink activity of the embedded client. The
+  // observer keeps receiving begin-frame until it is destroyed.
+  RequestBeginFrames(FrameSinkObserver observer);
 };