Plumb gesture source value through Blink.

third_party/WebKit/public/web/WebInputEvent.h

 /*
  * Copyright (C) 2009 Google 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:
  *
  *     * 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
@@ skipping 522 matching lines @@
             float scale;
         } pinchUpdate;
     } data;
 
     WebGestureEvent()
         : WebInputEvent(sizeof(WebGestureEvent))
         , x(0)
         , y(0)
         , globalX(0)
         , globalY(0)
+        , sourceDevice(WebGestureDeviceUninitialized)
         , resendingPluginId(-1)
     {
         memset(&data, 0, sizeof(data));
     }
 };
 
 // WebTouchEvent --------------------------------------------------------------
 
 // TODO(e_hakkinen): Replace with WebPointerEvent. crbug.com/508283
 class WebTouchEvent : public WebInputEvent {
@@ skipping 28 matching lines @@
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif