Use Persistent::Reset.

chrome/renderer/extensions/scoped_persistent.h

 // Copyright 2013 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 CHROME_RENDERER_EXTENSIONS_SCOPED_PERSISTENT_H_
 #define CHROME_RENDERER_EXTENSIONS_SCOPED_PERSISTENT_H_
 
 #include "base/logging.h"
 #include "v8/include/v8.h"
 
 namespace extensions {
 
 // A v8::Persistent handle to a V8 value which destroys and clears the
 // underlying handle on destruction.
 template <typename T>
 class ScopedPersistent {
  public:
   ScopedPersistent() {
   }
 
   explicit ScopedPersistent(v8::Handle<T> handle) {
     reset(handle);
   }
 
   ~ScopedPersistent() {
     reset();
   }
 
   void reset(v8::Handle<T> handle) {
     reset();

[jochen (gone - plz use gerrit), 2013/05/13 14:07:40]

this call is not needed anymore, right?

[marja, 2013/05/13 14:16:04]

Done.

-    handle_ = v8::Persistent<T>::New(GetIsolate(handle), handle);
+    handle_.Reset(GetIsolate(handle), handle);
   }
 
   void reset() {
     if (handle_.IsEmpty())
       return;
     handle_.Dispose(GetIsolate(handle_));

[jochen (gone - plz use gerrit), 2013/05/13 14:07:40]

can this now be something like Reset(GetIsolate(), NULL)?

[marja, 2013/05/13 14:16:04]

We can Reset to an empty handle, but not NULL, so not changing this, as
discussed.

     handle_.Clear();
   }
 
   v8::Persistent<T> operator->() const {
     return handle_;
   }
 
   v8::Persistent<T> get() const {
     return handle_;
   }
@@ skipping 18 matching lines @@
   }
 
   v8::Persistent<T> handle_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedPersistent);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_RENDERER_EXTENSIONS_SCOPED_PERSISTENT_H_