Touchpad scroll latching enabled for Mac behind flag.

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 561 matching lines @@
       ScrollUnits deltaUnits;
       // 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 generate the proper
       // GSB/GSU/GSE matching sequences. This is a temporary so that a future
       // GSB will generate a hit test so latching behavior is avoided
       // until crbug.com/526463 is fully implemented.
       bool synthetic;
+      // True if this event could be followed by a fling.
+      bool flingMightHappenNext;

[tdresser, 2016/11/14 16:02:29]

mayPrecedeFling? Or use flingMightHappenNext throughout.

[sahel, 2016/11/18 16:13:58]

Done.

     } scrollEnd;
 
     struct {
       float velocityX;
       float velocityY;
       // If true, this event will skip hit testing to find a scroll
       // target and instead just scroll the viewport.
       bool targetViewport;
     } flingStart;
 
@@ skipping 58 matching lines @@
         movedBeyondSlopRegion(false),
         touchStartOrFirstTouchMove(false),
         uniqueTouchEventId(0) {}
 };
 
 #pragma pack(pop)
 
 }  // namespace blink
 
 #endif