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

services/ui/public/interfaces/window_tree.mojom

 // Copyright 2014 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 ui.mojom;
 
 import "cc/ipc/frame_sink_id.mojom";
+import "cc/ipc/frame_sink_manager.mojom";
 import "cc/ipc/local_surface_id.mojom";
 import "cc/ipc/surface_id.mojom";
 import "cc/ipc/surface_info.mojom";
 import "cc/ipc/mojo_compositor_frame_sink.mojom";
 import "services/ui/public/interfaces/cursor/cursor.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
 import "services/ui/public/interfaces/mus_constants.mojom";
 import "services/ui/public/interfaces/window_manager.mojom";
 import "services/ui/public/interfaces/window_manager_constants.mojom";
 import "services/ui/public/interfaces/window_tree_constants.mojom";
@@ skipping 86 matching lines @@
   StartPointerWatcher(bool want_moves);
 
   // Stops the pointer watcher for all events.
   StopPointerWatcher();
 
   // Sets the specified bounds of the specified window. The window will paint
   // the frame in the provided |local_frame_id|, if any.
   SetWindowBounds(uint32 change_id, uint32 window_id, gfx.mojom.Rect bounds,
                   cc.mojom.LocalSurfaceId? local_surface_id);
 
+  // Requests to be notified of begin-frame messages for the client window
+  // embedded in |window_id|.
+  RequestBeginFrames(uint32 window_id, cc.mojom.FrameSinkObserver observer);

[sky, 2017/05/14 16:26:58]

The browser and renderer already have a more direct communication channel. Can't
they communicate additional information over that channel rather than modifying
the ui service? In other words, why can't the renderer tell the browser about
frames directly?

+
   // Sets the client area of the specified window. The client area is specified
   // by way of insets. Everything outside of the insets, and not in
   // |additional_client_areas| is considered non-client area.
   // TODO(sky): convert additional_client_areas to a path.
   SetClientArea(uint32 window_id,
                 gfx.mojom.Insets insets,
                 array<gfx.mojom.Rect>? additional_client_areas);
 
   // Mouse events outside a hit test mask do not hit the window. The |mask| is
   // in window local coordinates. Pass null to clear the mask.
@@ skipping 406 matching lines @@
   // See description of WindowManager for details.
   GetWindowManager(associated WindowManager& internal);
 };
 
 // Mus provides this interface as a way for clients to connect and obtain a
 // WindowTree handle with a supplied WindowTreeClient handle. The
 // WindowTreeClient has no roots, use NewTopLevelWindow() to create one.
 interface WindowTreeFactory {
   CreateWindowTree(WindowTree& tree_request, WindowTreeClient client);
 };