content: Cleanup class/struct forward declarations

content/browser/host_zoom_level_context.h

 // Copyright 2014 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_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_
 #define CONTENT_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "content/browser/host_zoom_map_impl.h"
 #include "content/public/browser/zoom_level_delegate.h"
 
-class PrefService;
-
 namespace content {
 struct HostZoomLevelContextDeleter;
 
 // This class manages a HostZoomMap and associates it with a ZoomLevelDelegate,
 // if one is provided. It also serves to keep the zoom level machinery details
 // separate from the owning StoragePartitionImpl.
 class HostZoomLevelContext
     : public base::RefCountedThreadSafe<HostZoomLevelContext,
                                         HostZoomLevelContextDeleter> {
  public:
@@ skipping 26 matching lines @@
 
 struct HostZoomLevelContextDeleter {
   static void Destruct(const HostZoomLevelContext* context) {
     context->DeleteOnCorrectThread();
   }
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_