Actually free plugin implement vars when running out of process when the

ppapi/proxy/proxy_object_var.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_PROXY_OBJECT_VAR_H_
 #define PPAPI_PROXY_PROXY_OBJECT_VAR_H_
 
 #include "base/compiler_specific.h"
 #include "ppapi/shared_impl/var.h"
 
@@ skipping 13 matching lines @@
 
   virtual ~ProxyObjectVar();
 
   // Var overrides.
   virtual ProxyObjectVar* AsProxyObjectVar() OVERRIDE;
   virtual PP_VarType GetType() const OVERRIDE;
 
   proxy::PluginDispatcher* dispatcher() const { return dispatcher_; }
   int32 host_var_id() const { return host_var_id_; }
 
+  void* user_data() const { return user_data_; }
+  void set_user_data(void* ud) { user_data_ = ud; }
+
   // Expose AssignVarID on Var so the PluginResourceTracker can call us when
   // it's creating IDs.
   void AssignVarID(int32 id);
 
  private:
   proxy::PluginDispatcher* dispatcher_;
   int32 host_var_id_;
 
+  // When this object is created as representing a var implemented by the
+  // plugin, this stores the user data so that we can look it up later. See
+  // PluginVarTracker.
+  void* user_data_;
+
   DISALLOW_COPY_AND_ASSIGN(ProxyObjectVar);
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_PROXY_OBJECT_VAR_H_