Replace uses of v8::Persistent with ScopedPersistent.

third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h

Index: third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h b/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
index c28339917b31265d43dfcc179d910c5f8251116c..4005f5512bb67e207e112d1cb32baddf1ce2046d 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
+++ b/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
@@ -72,6 +72,13 @@ public:
         m_handle.SetWeak(parameters, callback, type);
     }
 
+    // Turns this handle into a weak phantom handle without
+    // finalization callback.
+    void setPhantom()
+    {
+        m_handle.SetWeak();
+    }
+
     void clearWeak()
     {
         m_handle.template ClearWeak<void>();