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

cc/animation/scroll_offset_animation_curve.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 "cc/animation/scroll_offset_animation_curve.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/logging.h"
@@ skipping 96 matching lines @@
 bool ScrollOffsetAnimationCurve::HasSetInitialValue() const {
   return has_set_initial_value_;
 }
 
 void ScrollOffsetAnimationCurve::ApplyAdjustment(
     const gfx::Vector2dF& adjustment) {
   initial_value_ = ScrollOffsetWithDelta(initial_value_, adjustment);
   target_value_ = ScrollOffsetWithDelta(target_value_, adjustment);
 }
 
+void ScrollOffsetAnimationCurve::AdjustDuration(base::TimeDelta adjustment) {
+  base::TimeDelta old_duration = total_animation_duration_ - last_retarget_;
+  base::TimeDelta new_duration = old_duration - adjustment;
+  if (new_duration <= base::TimeDelta())
+    new_duration = base::TimeDelta();
+  total_animation_duration_ -= old_duration - new_duration;
+}
+
 gfx::ScrollOffset ScrollOffsetAnimationCurve::GetValue(
     base::TimeDelta t) const {
   base::TimeDelta duration = total_animation_duration_ - last_retarget_;
   t -= last_retarget_;
 
+  if (t >= duration)
+    return target_value_;
+
   if (t <= base::TimeDelta())
     return initial_value_;
 
-  if (t >= duration)
-    return target_value_;
-
   double progress = timing_function_->GetValue(TimeUtil::Divide(t, duration));
   return gfx::ScrollOffset(
       gfx::Tween::FloatValueBetween(
           progress, initial_value_.x(), target_value_.x()),
       gfx::Tween::FloatValueBetween(
           progress, initial_value_.y(), target_value_.y()));
 }
 
 base::TimeDelta ScrollOffsetAnimationCurve::Duration() const {
   return total_animation_duration_;
@@ skipping 88 matching lines @@
       (MaximumDimension(old_delta) / MaximumDimension(new_delta));
 
   initial_value_ = current_position;
   target_value_ = new_target;
   total_animation_duration_ = base::TimeDelta::FromSecondsD(t + new_duration);
   last_retarget_ = base::TimeDelta::FromSecondsD(t);
   timing_function_ = EaseOutWithInitialVelocity(new_normalized_velocity);
 }
 
 }  // namespace cc