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

ui/aura/mus/window_tree_host_mus.cc

 // 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.
 
 #include "ui/aura/mus/window_tree_host_mus.h"
 
 #include "base/memory/ptr_util.h"
 #include "ui/aura/env.h"
 #include "ui/aura/mus/input_method_mus.h"
 #include "ui/aura/mus/window_port_mus.h"
@@ skipping 131 matching lines @@
 }
 
 void WindowTreeHostMus::SetHitTestMask(const base::Optional<gfx::Rect>& rect) {
   delegate_->OnWindowTreeHostHitTestMaskWillChange(this, rect);
 }
 
 void WindowTreeHostMus::DeactivateWindow() {
   delegate_->OnWindowTreeHostDeactivateWindow(this);
 }
 
+void WindowTreeHostMus::StackAbove(Window* window) {
+  delegate_->OnWindowTreeHostStackAbove(this, window);
+}
+
 void WindowTreeHostMus::StackAtTop() {
   delegate_->OnWindowTreeHostStackAtTop(this);
 }
 
 display::Display WindowTreeHostMus::GetDisplay() const {
   display::Display display;
   display::Screen::GetScreen()->GetDisplayWithDisplayId(display_id_, &display);
   return display;
 }
 
@@ skipping 27 matching lines @@
 void WindowTreeHostMus::OnCloseRequest() {
   OnHostCloseRequested();
 }
 
 gfx::ICCProfile WindowTreeHostMus::GetICCProfileForCurrentDisplay() {
   // TODO: This should read the profile from mus. crbug.com/647510
   return gfx::ICCProfile();
 }
 
 }  // namespace aura