Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

components/mus/public/cpp/tests/window_server_test_base.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 "components/mus/public/cpp/tests/window_server_test_base.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/test_timeouts.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_tree_connection.h"
 #include "components/mus/public/cpp/window_tree_host_factory.h"
-#include "mojo/shell/public/cpp/application_impl.h"
+#include "mojo/shell/public/cpp/shell.h"
 
 namespace mus {
 namespace {
 
 base::RunLoop* current_run_loop = nullptr;
 
 void TimeoutRunLoop(const base::Closure& timeout_task, bool* timeout) {
   CHECK(current_run_loop);
   *timeout = true;
   timeout_task.Run();
@@ skipping 33 matching lines @@
     return false;
 
   current_run_loop->Quit();
   current_run_loop = nullptr;
   return true;
 }
 
 void WindowServerTestBase::SetUp() {
   ApplicationTestBase::SetUp();
 
-  CreateWindowTreeHost(application_impl(), this, &host_, this);
+  CreateWindowTreeHost(shell(), this, &host_, this);
 
   ASSERT_TRUE(DoRunLoopWithTimeout());  // RunLoop should be quit by OnEmbed().
   std::swap(window_manager_, most_recent_connection_);
 }
 
 mojo::ApplicationDelegate* WindowServerTestBase::GetApplicationDelegate() {
   return this;
 }
 
 bool WindowServerTestBase::AcceptConnection(
@@ skipping 46 matching lines @@
 
 void WindowServerTestBase::Create(
     mojo::ApplicationConnection* connection,
     mojo::InterfaceRequest<mojom::WindowTreeClient> request) {
   WindowTreeConnection::Create(
       this, std::move(request),
       WindowTreeConnection::CreateType::DONT_WAIT_FOR_EMBED);
 }
 
 }  // namespace mus