PPAPI: Reduce string copying in SerializedVar.

ppapi/proxy/plugin_var_serialization_rules.h

Index: ppapi/proxy/plugin_var_serialization_rules.h
diff --git a/ppapi/proxy/plugin_var_serialization_rules.h b/ppapi/proxy/plugin_var_serialization_rules.h
index 6bd96380c279e4dabf0ebedc66b1024e35bb993f..d18d44fb7ecbc9593cf3251a7b93abece8ac7763 100644
--- a/ppapi/proxy/plugin_var_serialization_rules.h
+++ b/ppapi/proxy/plugin_var_serialization_rules.h
@@ -22,15 +22,17 @@ class PluginVarSerializationRules : public VarSerializationRules {
   ~PluginVarSerializationRules();
 
   // 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);