Add support for touch-action: pinch-zoom.

third_party/WebKit/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 537 matching lines @@
             // If true, this event will skip hit testing to find a scroll
             // target and instead just scroll the viewport.
             bool targetViewport;
             // The state of inertial phase scrolling. OSX has unique phases for normal and
             // momentum scroll events. Should always be UnknownMomentumPhase for touch based
             // input as it generates GestureFlingStart instead.
             InertialPhaseState inertialPhase;
             // True if this event was synthesized in order to force a hit test; avoiding scroll
             // latching behavior until crbug.com/526463 is fully implemented.
             bool synthetic;
+
+            // number of pointers down.
+            int pointerCount;
         } scrollBegin;
 
         struct {
             float deltaX;
             float deltaY;
             float velocityX;
             float velocityY;
             // Whether any previous GestureScrollUpdate in the current scroll
             // sequence was suppressed (e.g., the causal touchmove was
             // preventDefault'ed). This bit is particularly useful for
@@ skipping 97 matching lines @@
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif