content: Cleanup class/struct forward declarations

content/public/browser/host_zoom_map.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 CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_
 #define CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/callback_list.h"
 #include "content/common/content_export.h"
 #include "url/gurl.h"
 
 namespace content {
 
 class NavigationEntry;
 class BrowserContext;
-class ResourceContext;
 class SiteInstance;
 class WebContents;
 
 // Maps hostnames to custom zoom levels.  Written on the UI thread and read on
 // any thread.  One instance per browser context. Must be created on the UI
 // thread, and it'll delete itself on the UI thread as well.
 // Zoom can be defined at three levels: default zoom, zoom for host, and zoom
 // for host with specific scheme. Setting any of the levels leaves settings
 // for other settings intact. Getting the zoom level starts at the most
 // specific setting and progresses to the less specific: first the zoom for the
@@ skipping 141 matching lines @@
   virtual std::unique_ptr<Subscription> AddZoomLevelChangedCallback(
       const ZoomLevelChangedCallback& callback) = 0;
 
  protected:
   virtual ~HostZoomMap() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_