use enum to specify deviceSource for fling animation

Source/web/WebInputEventFactoryMac.mm

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2006-2009 Google Inc.
  *
  * 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
@@ skipping 1119 matching lines @@
     setWebEventLocationFromEventInView(&temp, event, view);
     result.x = temp.x;
     result.y = temp.y;
     result.globalX = temp.globalX;
     result.globalY = temp.globalY;
 
     result.modifiers = modifiersFromEvent(event);
     result.timeStampSeconds = [event timestamp];
 
     // MacOS X gestures are used only for pinch support.
-    result.sourceDevice = WebGestureEvent::Touchpad;
+    result.sourceDevice = WebGestureDeviceTouchpad;
     switch ([event type]) {
     case NSEventTypeMagnify:
         result.type = WebInputEvent::GesturePinchUpdate;
         result.data.pinchUpdate.scale = [event magnification] + 1.0;
         break;
     default:
         ASSERT_NOT_REACHED();
         result.type = WebInputEvent::Undefined;
     }
 
     return result;
 }
 
 } // namespace blink