Populates sourceDevice attribute into TouchEvent

Source/core/events/TouchEvent.h

 /*
  * Copyright 2008, The Android Open Source Project
  * Copyright (C) 2012 Research In Motion Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *  * Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *  * Redistributions in binary form must reproduce the above copyright
@@ skipping 21 matching lines @@
 #include "core/events/MouseRelatedEvent.h"
 #include "core/dom/TouchList.h"
 
 namespace blink {
 
 class CORE_EXPORT TouchEvent final : public UIEventWithKeyState {
     DEFINE_WRAPPERTYPEINFO();
 public:
     virtual ~TouchEvent();
 
+    // We only initialize sourceDevice when we create TouchEvent from EventHandler, null if it is from JavaScript.
     static PassRefPtrWillBeRawPtr<TouchEvent> create()
     {
         return adoptRefWillBeNoop(new TouchEvent);
     }
     static PassRefPtrWillBeRawPtr<TouchEvent> create(TouchList* touches,
         TouchList* targetTouches, TouchList* changedTouches,
         const AtomicString& type, PassRefPtrWillBeRawPtr<AbstractView> view,
         bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, bool cancelable, bool causesScrollingIfUncanceled,
         double uiCreateTime = 0)
     {
@@ skipping 47 matching lines @@
     explicit TouchEventDispatchMediator(PassRefPtrWillBeRawPtr<TouchEvent>);
     TouchEvent& event() const;
     virtual bool dispatchEvent(EventDispatcher&) const override;
 };
 
 DEFINE_EVENT_TYPE_CASTS(TouchEvent);
 
 } // namespace blink
 
 #endif // TouchEvent_h