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

services/ui/ws/window_tree.cc

 // 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.
 
 #include "services/ui/ws/window_tree.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 1555 matching lines @@
   bool success = access_policy_->CanSetWindowBounds(window);
   if (success) {
     Operation op(this, window_server_, OperationType::SET_WINDOW_BOUNDS);
     window->SetBounds(bounds, local_surface_id);
   } else {
     DVLOG(1) << "SetWindowBounds failed (access denied)";
   }
   client()->OnChangeCompleted(change_id, success);
 }
 
+void WindowTree::RequestBeginFrames(Id window_id,
+                                    cc::mojom::FrameSinkObserverPtr observer) {
+  ServerWindow* window = GetWindowByClientId(ClientWindowId(window_id));
+  // This client must own |window_id| if it wants to be able to add a frame sink
+  // observer.
+  if (!window || window->id().client_id != id_)
+    return;
+  // This makes no sense if |window| is not embedding a client.
+  if (!window_server_->GetTreeWithRoot(window))
+    return;
+  window->GetOrCreateCompositorFrameSinkManager()->RequestBeginFrames(
+      std::move(observer));
+}
+
 void WindowTree::SetWindowVisibility(uint32_t change_id,
                                      Id transport_window_id,
                                      bool visible) {
   client()->OnChangeCompleted(
       change_id,
       SetWindowVisibility(ClientWindowId(transport_window_id), visible));
 }
 
 void WindowTree::SetWindowProperty(
     uint32_t change_id,
@@ skipping 897 matching lines @@
   client()->OnCompleteDrop(client_window_id.id, event_flags, cursor_offset,
                            effect_bitmask, callback);
 }
 
 void WindowTree::PerformOnDragDropDone() {
   client()->OnDragDropDone();
 }
 
 }  // namespace ws
 }  // namespace ui