Add delta hint fields to WebGestureEvent for scroll begin
Add delta hint fields to WebGestureEvent for scroll begin

We need to know the direction of motion when a scroll starts for touch-action
pan-x/pan-y support.  At the moment there's no need to plumb this into blink
(PlatformGestureEvent), but we need it in WebGestureEvent since that's the
common event type used by Android and Aura and consumed by chromium's
InputRouter.

Note that on Aura this information is redundant with the delta in the first
scroll update event.  But on Android it's not, and in fact an unbounded amont
of time may pass from the GestureScrollBegin to the first GestureScrollUpdate.

BUG=321643

Review URL: https://codereview.chromium.org/114723003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@164022 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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