chrome: Cleanup class/struct forward declarations

chrome/browser/plugins/plugin_observer.h

 // Copyright (c) 2012 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 CHROME_BROWSER_PLUGINS_PLUGIN_OBSERVER_H_
 #define CHROME_BROWSER_PLUGINS_PLUGIN_OBSERVER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/common/features.h"
 #include "components/component_updater/component_updater_service.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 #if BUILDFLAG(ENABLE_PLUGIN_INSTALLATION)
 #include <map>
 #endif
 
-class GURL;
-class PluginFinder;
-class PluginMetadata;
-
 #if BUILDFLAG(ENABLE_PLUGIN_INSTALLATION)
-class PluginInstaller;
 class PluginPlaceholderHost;
 #endif
 
 namespace content {
 class WebContents;
 }
 
-namespace infobars {
-class InfoBarDelegate;
-}
-
 class PluginObserver : public content::WebContentsObserver,
                        public content::WebContentsUserData<PluginObserver> {
  public:
   ~PluginObserver() override;
 
   // content::WebContentsObserver implementation.
   void PluginCrashed(const base::FilePath& plugin_path,
                      base::ProcessId plugin_pid) override;
   bool OnMessageReceived(const IPC::Message& message,
                          content::RenderFrameHost* render_frame_host) override;
@@ skipping 27 matching lines @@
 
   // Stores all ComponentObservers, keyed by their routing ID.
   std::map<int, std::unique_ptr<ComponentObserver>> component_observers_;
 
   base::WeakPtrFactory<PluginObserver> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginObserver);
 };
 
 #endif  // CHROME_BROWSER_PLUGINS_PLUGIN_OBSERVER_H_