Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/modules/device_orientation/DeviceMotionEvent.h

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 40 matching lines @@
 
     DeviceMotionData* deviceMotionData() const { return m_deviceMotionData.get(); }
 
     DeviceAcceleration* acceleration();
     DeviceAcceleration* accelerationIncludingGravity();
     DeviceRotationRate* rotationRate();
     double interval(bool& isNull) const;
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     DeviceMotionEvent();
     DeviceMotionEvent(const AtomicString& eventType, DeviceMotionData*);
 
-    RefPtrWillBePersistent<DeviceMotionData> m_deviceMotionData;
-
-    RefPtrWillBePersistent<DeviceAcceleration> m_acceleration;
-    RefPtrWillBePersistent<DeviceAcceleration> m_accelerationIncludingGravity;
-    RefPtrWillBePersistent<DeviceRotationRate> m_rotationRate;
+    RefPtrWillBeMember<DeviceMotionData> m_deviceMotionData;

[tkent, 2014/02/26 08:14:03]

I have a concern about changes like this.

After this change, applying real Oilpan types in modules/device_orientation
would not be a simple task.
* Need to consume time to distinguish between module-related and event-related.
* Need to introduce PersistentWillBeMember transition type.

[haraken, 2014/02/26 08:18:30]

Good point. The concern is valid. However, we cannot use persistent handles in
garbage-collected objects (because they will cause leaks).

Mads: Do you have any idea to address the issue?

+    RefPtrWillBeMember<DeviceAcceleration> m_acceleration;
+    RefPtrWillBeMember<DeviceAcceleration> m_accelerationIncludingGravity;
+    RefPtrWillBeMember<DeviceRotationRate> m_rotationRate;
 };
 
 DEFINE_TYPE_CASTS(DeviceMotionEvent, Event, event, event->interfaceName() == EventNames::DeviceMotionEvent, event.interfaceName() == EventNames::DeviceMotionEvent);
 
 } // namespace WebCore
 
 #endif // DeviceMotionEvent_h