Cleanup: Remove unneeded forward declarations in ppapi.

ppapi/native_client/src/shared/ppapi_proxy/plugin_resource_tracker.h

 // Copyright (c) 2011 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 WEBKIT_GLUE_PLUGINS_PEPPER_RESOURCE_TRACKER_H_
 #define WEBKIT_GLUE_PLUGINS_PEPPER_RESOURCE_TRACKER_H_
 
 #include <map>
 #include <utility>
 
 #include "native_client/src/include/nacl_base.h"
 #include "native_client/src/include/ref_counted.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_module.h"
 #include "ppapi/c/pp_resource.h"
 
 namespace ppapi_proxy {
 
-class PluginInstance;
 class PluginResource;
 
 // This class maintains a global list of all live pepper resources. It allows
 // us to check resource ID validity and to map them to a specific module.
 //
 // This object is threadsafe.
 class PluginResourceTracker {
  public:
   // Returns the pointer to the singleton object.
   static PluginResourceTracker* Get() {
@@ skipping 51 matching lines @@
   };
   typedef std::map<PP_Resource, ResourceAndRefCounts> ResourceMap;
   ResourceMap live_resources_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginResourceTracker);
 };
 
 }  // namespace ppapi_proxy
 
 #endif  // WEBKIT_GLUE_PLUGINS_PEPPER_RESOURCE_TRACKER_H_
-