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

webkit/plugins/ppapi/host_var_tracker.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_HOST_VAR_TRACKER_H_
 #define WEBKIT_PLUGINS_PPAPI_HOST_VAR_TRACKER_H_
 
 #include <map>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/hash_tables.h"
 #include "base/memory/linked_ptr.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/shared_impl/function_group_base.h"
 #include "ppapi/shared_impl/resource_tracker.h"
 #include "ppapi/shared_impl/var_tracker.h"
 #include "webkit/plugins/webkit_plugins_export.h"
 
 typedef struct NPObject NPObject;
 
 namespace ppapi {
@@ skipping 32 matching lines @@
 
   // Forcibly deletes all np object vars for the given instance. Used for
   // instance cleanup.
   void ForceFreeNPObjectsForInstance(PP_Instance instance);
 
  private:
   // VarTracker implementation.
   virtual ::ppapi::ArrayBufferVar* CreateArrayBuffer(
       uint32 size_in_bytes) OVERRIDE;
 
-  typedef std::map<NPObject*, ::ppapi::NPObjectVar*> NPObjectToNPObjectVarMap;
+  // Clear the reference count of the given object and remove it from
+  // live_vars_.
+  void ForceReleaseNPObject(const base::WeakPtr< ::ppapi::NPObjectVar>& object);
+
+  typedef std::map<NPObject*, base::WeakPtr< ::ppapi::NPObjectVar> >
+      NPObjectToNPObjectVarMap;
 
   // Lists all known NPObjects, first indexed by the corresponding instance,
   // then by the NPObject*. This allows us to look up an NPObjectVar given
   // these two pieces of information.
   //
   // The instance map is lazily managed, so we'll add the
   // NPObjectToNPObjectVarMap lazily when the first NPObject var is created,
   // and delete it when it's empty.
   typedef std::map<PP_Instance, linked_ptr<NPObjectToNPObjectVarMap> >
       InstanceMap;
   InstanceMap instance_map_;
 
   DISALLOW_COPY_AND_ASSIGN(HostVarTracker);
 };
 
 }  // namespace ppapi
 }  // namespace webkit
 
 #endif  // WEBKIT_PLUGINS_PPAPI_HOST_VAR_TRACKER_H_