Re-land http://codereview.chromium.org/9403039/, r124106

webkit/plugins/ppapi/npobject_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 WEBKIT_PLUGINS_PPAPI_NPOBJECT_VAR_H_
 #define WEBKIT_PLUGINS_PPAPI_NPOBJECT_VAR_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/shared_impl/var.h"
 #include "webkit/plugins/webkit_plugins_export.h"
 
 typedef struct NPObject NPObject;
 typedef struct _NPVariant NPVariant;
 typedef void* NPIdentifier;
 
 namespace ppapi {
 
 // NPObjectVar -----------------------------------------------------------------
 
 // Represents a JavaScript object Var. By itself, this represents random
 // NPObjects that a given plugin (identified by the resource's module) wants to
 // reference. If two different modules reference the same NPObject (like the
 // "window" object), then there will be different NPObjectVar's (and hence
 // PP_Var IDs) for each module. This allows us to track all references owned by
 // a given module and free them when the plugin exits independently of other
 // plugins that may be running at the same time.
-class NPObjectVar : public Var {
+class NPObjectVar : public Var,
+                    public base::SupportsWeakPtr<NPObjectVar> {
  public:
   // You should always use FromNPObject to create an NPObjectVar. This function
   // guarantees that we maintain the 1:1 mapping between NPObject and
   // NPObjectVar.
   NPObjectVar(PP_Instance instance, NPObject* np_object);
 
   virtual ~NPObjectVar();
 
   // Var overrides.
   virtual NPObjectVar* AsNPObjectVar() OVERRIDE;
@@ skipping 21 matching lines @@
   // Guaranteed non-NULL, this is the underlying object used by WebKit. We
   // hold a reference to this object.
   NPObject* np_object_;
 
   DISALLOW_COPY_AND_ASSIGN(NPObjectVar);
 };
 
 }  // namespace
 
 #endif  // WEBKIT_PLUGINS_PPAPI_NPOBJECT_VAR_H_