Reduce composited smooth scroll latency by a frame (also fixes latency UMAs).

cc/animation/animation_host.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 "cc/animation/animation_host.h"
 
 #include <algorithm>
 
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
@@ skipping 510 matching lines @@
 
 bool AnimationHost::HasTickingAnimationForTesting(ElementId element_id) const {
   auto element_animations = GetElementAnimationsForElementId(element_id);
   return element_animations ? element_animations->HasTickingAnimation() : false;
 }
 
 void AnimationHost::ImplOnlyScrollAnimationCreate(
     ElementId element_id,
     const gfx::ScrollOffset& target_offset,
     const gfx::ScrollOffset& current_offset,
-    base::TimeDelta delayed_by) {
+    base::TimeDelta delayed_by,
+    base::TimeDelta animation_start_offset) {
   DCHECK(scroll_offset_animations_impl_);
   scroll_offset_animations_impl_->ScrollAnimationCreate(
-      element_id, target_offset, current_offset, delayed_by);
+      element_id, target_offset, current_offset, delayed_by,
+      animation_start_offset);
 }
 
 bool AnimationHost::ImplOnlyScrollAnimationUpdateTarget(
     ElementId element_id,
     const gfx::Vector2dF& scroll_delta,
     const gfx::ScrollOffset& max_scroll_offset,
     base::TimeTicks frame_monotonic_time,
     base::TimeDelta delayed_by) {
   DCHECK(scroll_offset_animations_impl_);
   return scroll_offset_animations_impl_->ScrollAnimationUpdateTarget(
@@ skipping 29 matching lines @@
     const {
   return ticking_players_;
 }
 
 const AnimationHost::ElementToAnimationsMap&
 AnimationHost::element_animations_for_testing() const {
   return element_to_animations_map_;
 }
 
 }  // namespace cc