aura-mus: Implement DesktopWindowTreeHostMus::StackAbove().

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 "services/ui/public/interfaces/cursor.mojom";
 import "services/ui/public/interfaces/display/display.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
 import "services/ui/public/interfaces/window_manager_constants.mojom";
@@ skipping 173 matching lines @@
                     MoveLoopSource source,
                     gfx.mojom.Point cursor_location);
 
   // Asks the WindowManager to cancel any outstanding move loop on |change_id|.
   WmCancelMoveLoop(uint32 change_id);
 
   // Asks the WindowManager to change the activation from the current window
   // to the next. The window manager may completely ignore this message.
   WmDeactivateWindow(uint32 window_id);
 
+  // Asks the WindowMangaer to stack |above_id| in front of |below_id|.
+  WmStackAbove(uint32 change_id, uint32 above_id, uint32 below_id);
+
   // Asks the WindowManager to stack |window_id| as the first child of its
   // window manager owned parent.
   WmStackAtTop(uint32 change_id, uint32 window_id);
 
   // An accelerator registered via AddAccelerator() has been triggered. If
   // |ack_id| is non-zero the accelerator matches a PRE_TARGET and must be
   // acknowledged by WindowManagerClient::OnAcceleratorAck().
   OnAccelerator(uint32 ack_id, uint32 accelerator_id, ui.mojom.Event event);
 };
 
@@ skipping 47 matching lines @@
   WmSetNonClientCursor(uint32 window_id, Cursor cursor_id);
 
   // Response from WmCreateTopLevelWindow() informing the client of the id for
   // the new window.
   OnWmCreatedTopLevelWindow(uint32 change_id, uint32 window_id);
 
   // See description in WindowManager::OnAccelerator(). |ack_id| is the value
   // that was passed to OnAccelerator().
   OnAcceleratorAck(uint32 ack_id, EventResult event_result);
 };