Have mash_browser_tests recreate BackgroundServiceManager per test

ui/views/mus/aura_init.h

 // 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.
 
 #ifndef UI_VIEWS_MUS_AURA_INIT_H_
 #define UI_VIEWS_MUS_AURA_INIT_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 48 matching lines @@
            const std::string& resource_file,
            const std::string& resource_file_200 = std::string(),
            scoped_refptr<base::SingleThreadTaskRunner> io_task_runner = nullptr,
            Mode mode = Mode::UI);
   ~AuraInit();
 
   // Only valid if Mode::AURA_MUS was passed to constructor.
   MusClient* mus_client() { return mus_client_.get(); }
 
  private:
-  void InitializeResources(service_manager::Connector* connector);
+  // Attempts to initialize the resource bundle. Returns true if successful,
+  // otherwise false if resources cannot be loaded.
+  bool InitializeResources(service_manager::Connector* connector);
 
 #if defined(OS_LINUX)
   sk_sp<font_service::FontLoader> font_loader_;
 #endif
 
   const std::string resource_file_;
   const std::string resource_file_200_;
 
   std::unique_ptr<aura::Env> env_;
   std::unique_ptr<MusClient> mus_client_;
   std::unique_ptr<ViewsDelegate> views_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(AuraInit);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_AURA_INIT_H_