WebPrivatePtr: avoid creating temporary Persistent<> on assignment.

public/platform/WebPrivatePtr.h

Index: public/platform/WebPrivatePtr.h
diff --git a/public/platform/WebPrivatePtr.h b/public/platform/WebPrivatePtr.h
index 0d66cb4610fbd34e2eaf1c933de3552f5cd4e67c..6af8bfc7a1c6318de62e4d33425a3179fb848fe9 100644
--- a/public/platform/WebPrivatePtr.h
+++ b/public/platform/WebPrivatePtr.h
@@ -132,7 +132,7 @@ private:
 template<typename T>
 class PtrStorageImpl<T, RefCountedGarbageCollectedLifetime> : public PtrStorageImpl<T, GarbageCollectedLifetime> {
 public:
-    void assign(const PassRefPtr<T>& val) { PtrStorageImpl<T, GarbageCollectedLifetime>::assign(val.get()); }
+    void assign(const PassRefPtrWillBeRawPtr<T>& val) { PtrStorageImpl<T, GarbageCollectedLifetime>::assign(val.get()); }
 
     void assign(const PtrStorageImpl& other) { PtrStorageImpl<T, GarbageCollectedLifetime>::assign(other.get()); }
 };