Make Mac pinch thresholding apply only to zoom (Blink side)

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 480 matching lines @@
             float velocityY;
         } flingStart;
 
         struct {
             // If set to true, don't treat flingCancel
             // as a part of fling boost events sequence.
             bool preventBoosting;
         } flingCancel;
 
         struct {
+            bool zoomDisabled;

[Rick Byers, 2015/05/06 21:53:04]

nit: can we call this canZoom since it almost exactly parallels the
WebMouseWheelEvent::canScroll bit?  Also please add a comment saying why we need
this bit.

[ccameron, 2015/05/06 22:10:14]

I went with zoomDisabled so that the default value (the constructor memsets the
struct to 0) would match the default behavior. I can change it to canZoom, but
if I do, I'd like to update the constructor to initialize it to true then --
sound reasonable?

             float scale;
         } pinchUpdate;
     } data;
 
     WebGestureEvent()
         : WebInputEvent(sizeof(WebGestureEvent))
         , x(0)
         , y(0)
         , globalX(0)
         , globalY(0)
@@ skipping 36 matching lines @@
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif