Populates sourceDevice attribute into TouchEvent

Source/core/input/InputDevice.h

 // Copyright 2015 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 InputDevice_h
 #define InputDevice_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/CoreExport.h"
 #include "core/input/InputDeviceInit.h"
 
 namespace blink {
 
 class CORE_EXPORT InputDevice : public GarbageCollectedFinalized<InputDevice>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 
 public:
     ~InputDevice();
+
+    // This return a static local InputDevice pointer which has firesTouchEvents set to be true.
+    static InputDevice* touchEventInstance();
+
     static InputDevice* create(bool firesTouchEvents)
     {
         return new InputDevice(firesTouchEvents);
     }
 
     static InputDevice* create(
         const InputDeviceInit& initializer)
     {
         return new InputDevice(initializer);
     }
 
     bool firesTouchEvents() const { return m_firesTouchEvents; }
 
     DEFINE_INLINE_TRACE() { }
 
 private:
     InputDevice(bool firesTouchEvents);
     InputDevice(const InputDeviceInit&);
 
     // Whether this device dispatches touch events. This mainly lets developers
     // avoid handling both touch and mouse events dispatched for a single user
     // action.
     bool m_firesTouchEvents;
 };
 
 } // namespace blink
 
 #endif // InputDevice_h