Expose whether a ScrollUpdate is the first such in the sequence

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 438 matching lines @@
             // May be redundant with deltaX/deltaY in the first scrollUpdate.
             float deltaXHint;
             float deltaYHint;
         } 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
+            // determining whether the observed scroll update sequence captures
+            // the entirety of the generative motion.
+            // See comment at the top for why an int is used here instead of a bool.
+            int previousUpdateInSequencePrevented;
         } scrollUpdate;
 
         struct {
             float velocityX;
             float velocityY;
         } flingStart;
 
         struct {
             float scale;
         } pinchUpdate;
@@ skipping 33 matching lines @@
         , cancelable(true)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif