Fix smooth scroll animation flake on janky pages

cc/test/animation_test_common.cc

 // Copyright 2012 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/test/animation_test_common.h"
 
 #include "base/memory/ptr_util.h"
 #include "cc/animation/animation_host.h"
 #include "cc/animation/animation_id_provider.h"
 #include "cc/animation/animation_player.h"
 #include "cc/animation/element_animations.h"
 #include "cc/animation/keyframed_animation_curve.h"
+#include "cc/animation/scroll_offset_animation_curve.h"
 #include "cc/animation/timing_function.h"
 #include "cc/animation/transform_operations.h"
 #include "cc/base/time_util.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_impl.h"
 
 using cc::Animation;
 using cc::AnimationCurve;
 using cc::FloatKeyframe;
 using cc::KeyframedFloatAnimationCurve;
@@ skipping 186 matching lines @@
   double progress = TimeUtil::Divide(time, duration_);
   if (progress >= 1.0)
     progress = 1.0;
   return (1.0 - progress) * from_ + progress * to_;
 }
 
 std::unique_ptr<AnimationCurve> FakeFloatTransition::Clone() const {
   return base::WrapUnique(new FakeFloatTransition(*this));
 }
 
+int AddScrollOffsetAnimationToElementAnimations(ElementAnimations* target,
+                                                gfx::ScrollOffset initial_value,
+                                                gfx::ScrollOffset target_value,
+                                                bool impl_only) {
+  std::unique_ptr<ScrollOffsetAnimationCurve> curve(
+      ScrollOffsetAnimationCurve::Create(
+          target_value, CubicBezierTimingFunction::CreatePreset(
+                            CubicBezierTimingFunction::EaseType::EASE_IN_OUT)));
+  curve->SetInitialValue(initial_value);
+
+  int id = AnimationIdProvider::NextAnimationId();
+
+  std::unique_ptr<Animation> animation(Animation::Create(
+      std::move(curve), id, AnimationIdProvider::NextGroupId(),
+      TargetProperty::SCROLL_OFFSET));
+  animation->set_is_impl_only(impl_only);
+
+  target->AddAnimation(std::move(animation));
+
+  return id;
+}
+
 int AddOpacityTransitionToElementAnimations(ElementAnimations* target,
                                             double duration,
                                             float start_opacity,
                                             float end_opacity,
                                             bool use_timing_function) {
   return AddOpacityTransition(target, duration, start_opacity, end_opacity,
                               use_timing_function);
 }
 
 int AddAnimatedTransformToElementAnimations(ElementAnimations* target,
@@ skipping 172 matching lines @@
     ElementId element_id,
     scoped_refptr<AnimationTimeline> timeline,
     TargetProperty::Type target_property) {
   scoped_refptr<ElementAnimations> element_animations =
       timeline->animation_host()->GetElementAnimationsForElementId(element_id);
   DCHECK(element_animations);
   element_animations->AbortAnimations(target_property);
 }
 
 }  // namespace cc