extensions: Cleanup class/struct fwd declarations

extensions/test/background_page_watcher.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.
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "extensions/browser/process_manager_observer.h"
 
 namespace extensions {
 class Extension;
-class ExtensionHost;
 class ProcessManager;
 
 // Observes the background page load state of an extension. Use this in tests
 // which rely on a specific open or close state of a background page.
 class BackgroundPageWatcher : public ProcessManagerObserver {
  public:
   BackgroundPageWatcher(ProcessManager* process_manager,
                         const Extension* extension);
 
   ~BackgroundPageWatcher();
@@ skipping 24 matching lines @@
   ProcessManager* process_manager_;
   const std::string extension_id_;
   base::Closure quit_run_loop_;
   bool is_waiting_for_open_;
   bool is_waiting_for_close_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundPageWatcher);
 };
 
 }  // namespace extensions