Creates BackgroundShell and uses it in test

ui/views/mus/window_manager_connection.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/views/mus/window_manager_connection.h"
 
 #include <utility>
 
 #include "base/lazy_instance.h"
 #include "base/threading/thread_local.h"
@@ skipping 25 matching lines @@
   lazy_tls_ptr.Pointer()->Set(new WindowManagerConnection(shell));
 }
 
 // static
 WindowManagerConnection* WindowManagerConnection::Get() {
   WindowManagerConnection* connection = lazy_tls_ptr.Pointer()->Get();
   DCHECK(connection);
   return connection;
 }
 
+// static
+void WindowManagerConnection::Reset() {
+  delete Get();
+  lazy_tls_ptr.Pointer()->Set(nullptr);
+}
+
 mus::Window* WindowManagerConnection::NewWindow(
     const std::map<std::string, std::vector<uint8_t>>& properties) {
   return window_tree_connection_->NewTopLevelWindow(&properties);
 }
 
 WindowManagerConnection::WindowManagerConnection(mojo::Shell* shell)
     : shell_(shell), window_tree_connection_(nullptr) {
   window_tree_connection_.reset(
       mus::WindowTreeConnection::Create(this, shell_));
 
@@ skipping 24 matching lines @@
 NativeWidget* WindowManagerConnection::CreateNativeWidget(
     const Widget::InitParams& init_params,
     internal::NativeWidgetDelegate* delegate) {
   std::map<std::string, std::vector<uint8_t>> properties;
   NativeWidgetMus::ConfigurePropertiesForNewWindow(init_params, &properties);
   return new NativeWidgetMus(delegate, shell_, NewWindow(properties),
                              mus::mojom::SurfaceType::DEFAULT);
 }
 
 }  // namespace views