Only send the FrameSinkId to client when it is necessary

services/ui/public/interfaces/window_manager.mojom

 // Copyright 2015 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/local_surface_id.mojom";
 import "services/ui/public/interfaces/cursor/cursor.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
@@ skipping 135 matching lines @@
 
   // The window's title. Maps to aura::client::kTitleKey. Type: mojom::String
   const string kWindowTitle_Property = "prop:window-title";
 
   // End long lived properties. ------------------------------------------------
 
   // Called immediately when the WindowManager is obtained.
   OnConnect(uint16 client_id);
 
   // Called when a new display is added. |root| gives the root window specific
-  // to this WindowManager for |display|. |frame_sink_id| uniquely identifies
-  // the window manager in the frame sink manager. |local_surface_id| identifies
-  // the ID to use to submit CompositorFrames.
+  // to this WindowManager for |display|. |local_surface_id| identifies the ID
+  // to use to submit CompositorFrames.
   WmNewDisplayAdded(display.mojom.Display display,
                     WindowData root,
                     bool parent_drawn,
-                    cc.mojom.FrameSinkId frame_sink_id,
                     cc.mojom.LocalSurfaceId? local_surface_id);
 
   // Called when a display is removed. The root of the specified display is
   // still valid. It is expected the client calls DeleteWindow() shortly after
   // this with the root.
   WmDisplayRemoved(int64 display_id);
 
   // Called when a display is modified. The root of the specified display will
   // be resized by the WindowServer after this.
   WmDisplayModified(display.mojom.Display display);
@@ skipping 93 matching lines @@
 
   // See WindowTree for details on event dispatch.
   // This ignores any accelerators already defined with the same id or matcher.
   // Returns true if all accelerators were added successfully.
   AddAccelerators(array<WmAccelerator> accelerators) => (bool success);
   RemoveAccelerator(uint32 id);
 
   // Sets the root of a particular display. This is only applicable when the
   // WindowTree was created with a value of false for
   // |automatically_create_display_roots| (see
-  // WindowManagerWindowTreeFactory::CreateWindowTree() for details). On success
-  // this responds with the FrameSinkId of the root. On failure the FrameSinkId
-  // is not valid.
+  // WindowManagerWindowTreeFactory::CreateWindowTree() for details).
+  // Returns true on success.
   SetDisplayRoot(display.mojom.Display display,
                  WmViewportMetrics viewport_metrics,
                  bool is_primary_display,
-                 uint32 window_id) => (cc.mojom.FrameSinkId? frame_sink_id);
+                 uint32 window_id) => (bool success);
 
   // The window manager has completed a request with the specific change id.
   WmResponse(uint32 change_id, bool response);
 
   // The window manager has completed a SetBounds request with the specified
   // change id
   WmSetBoundsResponse(uint32 change_id);
 
   // Calls WindowTreeClient::RequestClose() on the embedded app at the
   // specified window.
@@ skipping 23 matching lines @@
   OnWmCreatedTopLevelWindow(uint32 change_id, uint32 window_id);
 
   // See description in WindowManager::OnAccelerator(). |ack_id| is the value
   // that was passed to OnAccelerator(). If the accelerator is a pre-target
   // handler and |event_result| is UNHANDLED, then |properties| is added to
   // the KeyEvent that is dispatched to the client with the focused window.
   OnAcceleratorAck(uint32 ack_id,
                    EventResult event_result,
                    map<string, array<uint8>> properties);
 };