Cleanup: Remove unneeded forward declarations in ppapi.

ppapi/proxy/host_var_serialization_rules.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 PPAPI_PROXY_HOST_VAR_SERIALIZATION_RULES_H_
 #define PPAPI_PROXY_HOST_VAR_SERIALIZATION_RULES_H_
 
+#include <string>
+
 #include "base/basictypes.h"
 #include "ppapi/c/pp_module.h"
 #include "ppapi/proxy/var_serialization_rules.h"
 
 struct PPB_Var;
 
 namespace ppapi {
 namespace proxy {
 
-class VarTracker;
-
 // Implementation of the VarSerializationRules interface for the host side.
 class HostVarSerializationRules : public VarSerializationRules {
  public:
   HostVarSerializationRules(const PPB_Var* var_interface,
                             PP_Module pp_module);
   ~HostVarSerializationRules();
 
   // VarSerialization implementation.
   virtual PP_Var SendCallerOwned(const PP_Var& var, std::string* str_val);
   virtual PP_Var BeginReceiveCallerOwned(const PP_Var& var,
@@ skipping 15 matching lines @@
   const PPB_Var* var_interface_;
   PP_Module pp_module_;
 
   DISALLOW_COPY_AND_ASSIGN(HostVarSerializationRules);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_HOST_VAR_SERIALIZATION_RULES_H_