Implement PointerEvent#dx

sky/engine/public/platform/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 194 matching lines @@
     enum Kind {
         Touch,
         Mouse,
         Stylus,
     };
 
     int pointer = 0;
     Kind kind = Touch;
     float x = 0;
     float y = 0;
-    float dx = 0;
-    float dy = 0;
     int buttons = 0;
     float pressure = 0;
     float pressureMin = 0;
     float pressureMax = 0;
     float distance = 0;
     float distanceMin = 0;
     float distanceMax = 0;
     float radiusMajor = 0;
     float radiusMinor = 0;
     float radiusMin = 0;
@@ skipping 104 matching lines @@
     {
         memset(&data, 0, sizeof(data));
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_PUBLIC_PLATFORM_WEBINPUTEVENT_H_