aura-mus: Implement stacking in DesktopWindowTreeHostMus.

ui/aura/test/mus/test_window_tree.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/test/mus/test_window_tree.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace aura {
 
@@ skipping 250 matching lines @@
                                       mojo::TextInputStatePtr state) {}
 
 void TestWindowTree::OnWindowInputEventAck(uint32_t event_id,
                                            ui::mojom::EventResult result) {
   EXPECT_FALSE(WasEventAcked(event_id));
   acked_events_.push_back({event_id, result});
 }
 
 void TestWindowTree::DeactivateWindow(uint32_t window_id) {}
 
+void TestWindowTree::StackAtTop(uint32_t change_id, uint32_t window_id) {}
+
 void TestWindowTree::GetWindowManagerClient(
     mojo::AssociatedInterfaceRequest<ui::mojom::WindowManagerClient> internal) {
 }
 
 void TestWindowTree::GetCursorLocationMemory(
     const GetCursorLocationMemoryCallback& callback) {
   callback.Run(mojo::ScopedSharedBufferHandle());
 }
 
 void TestWindowTree::PerformDragDrop(
     uint32_t change_id,
     uint32_t source_window_id,
     const std::unordered_map<std::string, std::vector<uint8_t>>& drag_data,
     uint32_t drag_operation) {
   OnChangeReceived(change_id);
 }
 
 void TestWindowTree::CancelDragDrop(uint32_t window_id) {}
 
 void TestWindowTree::PerformWindowMove(uint32_t change_id,
                                        uint32_t window_id,
                                        ui::mojom::MoveLoopSource source,
                                        const gfx::Point& cursor_location) {
   OnChangeReceived(change_id);
 }
 
 void TestWindowTree::CancelWindowMove(uint32_t window_id) {}
 
 }  // namespace aura