Adds ability for WindowManager to create display roots

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 252 matching lines @@
   // target window. The id is defined by the client and can be used to more
   // easily identify the accelerator's action.
   // Accelerator ids 1 << 31 and above are reserved for internal use.
 
   // 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).
+  SetDisplayRoot(int64 display_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.
   WmRequestClose(uint32 window_id);
@@ skipping 10 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);
 };