PPAPI: Reduce string copying in SerializedVar.

ppapi/proxy/host_var_serialization_rules.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 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/c/ppb_var.h"
 #include "ppapi/proxy/var_serialization_rules.h"
 
 namespace ppapi {
 namespace proxy {
 
 // Implementation of the VarSerializationRules interface for the host side.
 class HostVarSerializationRules : public VarSerializationRules {
  public:
   HostVarSerializationRules(PP_Module pp_module);
   ~HostVarSerializationRules();
 
   // VarSerialization implementation.
-  virtual PP_Var SendCallerOwned(const PP_Var& var, std::string* str_val);
+  virtual PP_Var SendCallerOwned(const PP_Var& var,
+                                 const std::string** str_ptr_out);
   virtual PP_Var BeginReceiveCallerOwned(const PP_Var& var,
-                                         const std::string* str_val,
+                                         scoped_ptr<std::string> str,
                                          Dispatcher* dispatcher);
   virtual void EndReceiveCallerOwned(const PP_Var& var);
   virtual PP_Var ReceivePassRef(const PP_Var& var,
-                                const std::string& str_val,
+                                scoped_ptr<std::string> str,
                                 Dispatcher* dispatcher);
-  virtual PP_Var BeginSendPassRef(const PP_Var& var, std::string* str_val);
+  virtual PP_Var BeginSendPassRef(const PP_Var& var,
+                                  const std::string** str_ptr_out);
   virtual void EndSendPassRef(const PP_Var& var, Dispatcher* dispatcher);
   virtual void ReleaseObjectRef(const PP_Var& var);
 
  private:
   // Converts the given var (which must be a VARTYPE_STRING) to the given
   // string object.
-  void VarToString(const PP_Var& var, std::string* str);
+  void VarToStringPtr(const PP_Var& var, const std::string** str);
 
   PP_Module pp_module_;
 
   DISALLOW_COPY_AND_ASSIGN(HostVarSerializationRules);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_HOST_VAR_SERIALIZATION_RULES_H_