Fix a crash related to PPAPI scripting.

ppapi/proxy/plugin_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_PLUGIN_VAR_SERIALIZATION_RULES_H_
 #define PPAPI_PROXY_PLUGIN_VAR_SERIALIZATION_RULES_H_
 
 #include "base/basictypes.h"
+#include "base/memory/weak_ptr.h"
 #include "ppapi/proxy/var_serialization_rules.h"
 
 namespace ppapi {
 namespace proxy {
 
+class PluginDispatcher;
 class PluginVarTracker;
 
-// Implementation of the VarSerialization interface for the plugin.
+// Implementation of the VarSerializationRules interface for the plugin.
 class PluginVarSerializationRules : public VarSerializationRules {
  public:
   // This class will use the given non-owning pointer to the var tracker to
   // handle object refcounting and string conversion.
-  PluginVarSerializationRules();
+  explicit PluginVarSerializationRules(
+      const base::WeakPtr<PluginDispatcher>& dispatcher);
   ~PluginVarSerializationRules();
 
   // VarSerialization implementation.
   virtual PP_Var SendCallerOwned(const PP_Var& var);
-  virtual PP_Var BeginReceiveCallerOwned(const PP_Var& var,
-                                         Dispatcher* dispatcher);
+  virtual PP_Var BeginReceiveCallerOwned(const PP_Var& var);
   virtual void EndReceiveCallerOwned(const PP_Var& var);
-  virtual PP_Var ReceivePassRef(const PP_Var& var, Dispatcher* dispatcher);
+  virtual PP_Var ReceivePassRef(const PP_Var& var);
   virtual PP_Var BeginSendPassRef(const PP_Var& var);
-  virtual void EndSendPassRef(const PP_Var& var, Dispatcher* dispatcher);
+  virtual void EndSendPassRef(const PP_Var& var);
   virtual void ReleaseObjectRef(const PP_Var& var);
 
  private:
   PluginVarTracker* var_tracker_;
 
+  // In most cases, |dispatcher_| won't be NULL.

[brettw, 2012/03/09 21:57:22]

Can you make it clear here the you should check the validity of the weak pointer
before using it?

"In most cases, |dispatcher_| won't be NULL, but you should always check before
using it."

[yzshen1, 2012/03/09 22:05:48]

Done.

+  // One scenario that it becomes NULL: A SerializedVar holds a ref to this
+  // object, and a sync message is issued. While waiting for the reply to the
+  // sync message, some incoming message causes the dispatcher to be destroyed.
+  // If that happens, we may leak references to object vars. Considering that
+  // scripting has been deprecated, this may not be a big issue.
+  base::WeakPtr<PluginDispatcher> dispatcher_;
+
   DISALLOW_COPY_AND_ASSIGN(PluginVarSerializationRules);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_PLUGIN_VAR_SERIALIZATION_RULES_H_