Touchpad scroll latching enabled for Mac behind flag.

third_party/WebKit/public/platform/WebGestureEvent.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebGestureEvent_h
 #define WebGestureEvent_h
 
 #include "WebGestureDevice.h"
 #include "WebInputEvent.h"
 
@@ skipping 114 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 will be followed by a fling.
+      bool precedesFling;
     } 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 17 matching lines @@
         globalY(0),
         sourceDevice(WebGestureDeviceUninitialized),
         resendingPluginId(-1) {}
 };
 
 #pragma pack(pop)
 
 }  // namespace blink
 
 #endif  // WebGestureEvent_h