Take MT jank into account when animating the scroll offset on CC

ui/events/blink/input_handler_proxy.cc

 // Copyright 2013 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 "ui/events/blink/input_handler_proxy.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 475 matching lines @@
     // TODO(jamesr): We don't properly handle scroll by page in the compositor
     // thread, so punt it to the main thread. http://crbug.com/236639
     result = DID_NOT_HANDLE;
     RecordMainThreadScrollingReasons(
         blink::WebGestureDeviceTouchpad,
         cc::MainThreadScrollingReason::kPageBasedScrolling);
 
   } else if (ShouldAnimate(wheel_event.hasPreciseScrollingDeltas)) {
     cc::InputHandler::ScrollStatus scroll_status =
         input_handler_->ScrollAnimated(gfx::Point(wheel_event.x, wheel_event.y),
-                                       scroll_delta);
+                                       scroll_delta, base::TimeDelta());
 
     RecordMainThreadScrollingReasons(
         blink::WebGestureDeviceTouchpad,
         scroll_status.main_thread_scrolling_reasons);
 
     switch (scroll_status.thread) {
       case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
         result = DID_HANDLE;
         break;
       case cc::InputHandler::SCROLL_IGNORED:
@@ skipping 111 matching lines @@
   }
   if (scroll_elasticity_controller_ && result != DID_NOT_HANDLE)
     HandleScrollElasticityOverscroll(gesture_event,
                                      cc::InputHandlerScrollResult());
 
   return result;
 }
 
 InputHandlerProxy::EventDisposition
 InputHandlerProxy::HandleGestureScrollUpdate(
-  const WebGestureEvent& gesture_event) {
+    const WebGestureEvent& gesture_event) {
 #ifndef NDEBUG
   DCHECK(expect_scroll_update_end_);
 #endif
   if (!gesture_scroll_on_impl_thread_ && !gesture_pinch_on_impl_thread_)
     return DID_NOT_HANDLE;
 
   cc::ScrollState scroll_state = CreateScrollStateForGesture(gesture_event);
   gfx::Point scroll_point(gesture_event.x, gesture_event.y);
   gfx::Vector2dF scroll_delta(-gesture_event.data.scrollUpdate.deltaX,
                               -gesture_event.data.scrollUpdate.deltaY);
 
   if (ShouldAnimate(gesture_event.data.scrollUpdate.deltaUnits !=
                     blink::WebGestureEvent::ScrollUnits::Pixels)) {
-    switch (input_handler_->ScrollAnimated(scroll_point, scroll_delta).thread) {
+    base::TimeDelta delay =
+        (base::TimeTicks::Now() -
+         (base::TimeTicks() +
+          base::TimeDelta::FromSecondsD(gesture_event.timeStampSeconds)));

[tdresser, 2016/08/25 15:55:54]

Math seems correct, though I might add a temporary here to make this prettier.

[ymalik, 2016/08/29 14:52:06]

Good tip, looks much prettier!

+    switch (input_handler_->ScrollAnimated(scroll_point, scroll_delta, delay)
+                .thread) {
       case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
         return DID_HANDLE;
       case cc::InputHandler::SCROLL_IGNORED:
         return DROP_EVENT;
       default:
         return DID_NOT_HANDLE;
     }
   }
   cc::InputHandlerScrollResult scroll_result =
       input_handler_->ScrollBy(&scroll_state);
@@ skipping 688 matching lines @@
   // is made asynchronously, to minimize divergence between main thread and
   // impl thread event handling paths.
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE,
       base::Bind(&InputScrollElasticityController::ObserveGestureEventAndResult,
                  scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
                  scroll_result));
 }
 
 }  // namespace ui