Add "targetViewport" to ScrollBegin and FlingStart

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 451 matching lines @@
         struct {
             float firstFingerWidth;
             float firstFingerHeight;
         } twoFingerTap;
 
         struct {
             // Initial motion that triggered the scroll.
             // May be redundant with deltaX/deltaY in the first scrollUpdate.
             float deltaXHint;
             float deltaYHint;
+            // True if the scroll is targeted to viewport.

[bokan, 2015/06/16 14:38:04]

I would make the comment more explicit that we'll skip hit testing. Something
along the lines of: "If true, this event will skip hit testing to find a scroll
target and, instead, scroll the viewport."

[hush (inactive), 2015/06/18 20:25:48]

Done.

+            bool targetViewport;
         } 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.
             bool previousUpdateInSequencePrevented;
             bool preventPropagation;
             bool inertial;
         } scrollUpdate;
 
         struct {
             float velocityX;
             float velocityY;
+            // True if the fling is targeted to viewport.
+            bool targetViewport;
         } flingStart;
 
         struct {
             // If set to true, don't treat flingCancel
             // as a part of fling boost events sequence.
             bool preventBoosting;
         } flingCancel;
 
         struct {
             bool zoomDisabled;
@@ skipping 46 matching lines @@
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif