Converts WindowTreeClientTest to be in terms of aura

ash/mus/window_manager_unittest.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 <map>
 #include <memory>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/macros.h"
@@ skipping 25 matching lines @@
 
   void DestroyWindowTreeHost() { window_tree_host_.reset(); }
 
  private:
   // aura::WindowTreeClientDelegate:
   void OnEmbed(
       std::unique_ptr<aura::WindowTreeHostMus> window_tree_host) override {
     window_tree_host_ = std::move(window_tree_host);
     run_loop_.Quit();
   }
-  void OnEmbedRootDestroyed(aura::Window* root) override {}
+  void OnEmbedRootDestroyed(
+      aura::WindowTreeHostMus* window_tree_host) override {}
   void OnLostConnection(aura::WindowTreeClient* client) override {}
   void OnPointerEventObserved(const ui::PointerEvent& event,
                               aura::Window* target) override {}
   aura::client::CaptureClient* GetCaptureClient() override {
     return wm_state_.capture_controller();
   }
   aura::PropertyConverter* GetPropertyConverter() override {
     return &property_converter_;
   }
 
@@ skipping 54 matching lines @@
   client.Embed(child_window, std::move(tree_client), 0u, base::Bind(&OnEmbed));
   aura::WindowTreeClient child_client(connector(), &window_tree_delegate,
                                       nullptr, std::move(tree_client_request));
   window_tree_delegate.WaitForEmbed();
   ASSERT_TRUE(!child_client.GetRoots().empty());
   window_tree_delegate.DestroyWindowTreeHost();
 }
 
 }  // namespace mus
 }  // namespace ash