Stop negating the overscroll velocity to enable the glow of main thread fling

content/renderer/input/render_widget_input_handler.cc

 // Copyright 2015 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.
 
 #include "content/renderer/input/render_widget_input_handler.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <utility>
 
@@ skipping 496 matching lines @@
 void RenderWidgetInputHandler::DidOverscrollFromBlink(
     const WebFloatSize& overscrollDelta,
     const WebFloatSize& accumulatedOverscroll,
     const WebFloatPoint& position,
     const WebFloatSize& velocity) {
   std::unique_ptr<DidOverscrollParams> params(new DidOverscrollParams());
   params->accumulated_overscroll = gfx::Vector2dF(
       accumulatedOverscroll.width, accumulatedOverscroll.height);
   params->latest_overscroll_delta =
       gfx::Vector2dF(overscrollDelta.width, overscrollDelta.height);
   // TODO(sataya.m): don't negate velocity once http://crbug.com/499743 is

[dtapuska, 2016/08/29 21:16:34]

Do we need to remove this comment? Is this partially fixed now?

[majidvp, 2016/08/31 19:39:40]

Overscroll glow logic expects to receive delta and velocity of scroll which are
in the same direction.

In the past this velocity here was the actual *gesture* velocity which needed to
be negated to get scroll behaviour. I did some digging and I think this bokan@
changed the semantic of this velocity here which is probably the point where the
glow effect broke: https://codereview.chromium.org/1755773002

So yes, please remove this TODO and close that bug as well :).

[bokan, 2016/08/31 21:04:30]

Yes, I believe that's correct.

   // fixed.
   params->current_fling_velocity =
-      gfx::Vector2dF(-velocity.width, -velocity.height);
+      gfx::Vector2dF(velocity.width, velocity.height);
   params->causal_event_viewport_point = gfx::PointF(position.x, position.y);
 
   // If we're currently handling an event, stash the overscroll data such that
   // it can be bundled in the event ack.
   if (handling_event_overscroll_) {
     *handling_event_overscroll_ = std::move(params);
     return;
   }
 
   delegate_->OnDidOverscroll(*params);
@@ skipping 21 matching lines @@
   if (pending_input_event_ack_) {
     TRACE_EVENT_ASYNC_END0("input",
                            "RenderWidgetInputHandler::ThrottledInputEventAck",
                            pending_input_event_ack_.get());
     delegate_->OnInputEventAck(std::move(pending_input_event_ack_));
   }
   total_input_handling_time_this_frame_ = base::TimeDelta();
 }
 
 }  // namespace content