Wheel scrolling with smooth scrolling enabled would cause an extra animation

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 2a191b83601ca69228ac505a0d4600f71897bdea..8c41ad50f37b3681329240628da5aeb8ecc16b74 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -597,10 +597,8 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureScrollBegin(
   } else if (smooth_scroll_enabled_ &&
              gesture_event.data.scrollBegin.deltaHintUnits ==
                  blink::WebGestureEvent::ScrollUnits::Pixels) {
-    gfx::Vector2dF scroll_delta(-gesture_event.data.scrollBegin.deltaXHint,
-                                -gesture_event.data.scrollBegin.deltaYHint);
     scroll_status = input_handler_->ScrollAnimated(
-        gfx::Point(gesture_event.x, gesture_event.y), scroll_delta);
+        gfx::Point(gesture_event.x, gesture_event.y), gfx::Vector2dF());

[tdresser, 2016/02/22 20:14:49]

Does this need to be a ScrollAnimated?
Can we just always call input_handler_->ScrollBegin instead?

[dtapuska, 2016/02/22 20:15:59]

I first attempted to do that and since a scroll animator isn't created it was
failing.

[ymalik, 2016/02/22 20:35:32]

Why do we need this branch to begin with if we're setting scroll delta to 0?
 
ScrollAnimated calls ScrollBegin, so where exactly does the call fail? 

[dtapuska, 2016/02/22 20:39:03]

ScrollAnimated is successful; but the next ScrollAnimated call doesn't work;
because it is already inside a scroll event.

We need to know if the GestureScrollBegin can scroll or not; I guess I could
call BeginScroll/EndScroll combination. Do you recommend that instead? Ideally I
want to get into the ScrollAnimationCreate code path inside
layer_tree_host_impl.cc

   } else {
     scroll_status =
         input_handler_->ScrollBegin(&scroll_state, cc::InputHandler::GESTURE);