Update from https://crrev.com/304121

cc/input/scroll_elasticity_helper.cc

+// Copyright 2014 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/input/scroll_elasticity_helper.h"
+
+#include "cc/layers/layer_impl.h"
+#include "cc/trees/layer_tree_host_impl.h"
+#include "cc/trees/layer_tree_impl.h"
+
+namespace cc {
+
+ScrollElasticityHelper::ScrollElasticityHelper(LayerTreeHostImpl* layer_tree)
+    : layer_tree_host_impl_(layer_tree), timer_active_(false) {
+}
+
+ScrollElasticityHelper::~ScrollElasticityHelper() {
+}
+
+bool ScrollElasticityHelper::AllowsHorizontalStretching() {
+  // The WebKit implementation has this interface because it is written in terms
+  // of overscrolling on a per-layer basis, not for the whole layer tree. In
+  // that implementation, this always returns true for the frame view's
+  // scrollable area.
+  // TODO(ccameron): This is function is redundant and may be removed.
+  return true;
+}
+
+bool ScrollElasticityHelper::AllowsVerticalStretching() {
+  // TODO(ccameron): This is function is redundant and may be removed.
+  return true;
+}
+
+gfx::Vector2dF ScrollElasticityHelper::StretchAmount() {
+  return stretch_offset_;
+}
+
+bool ScrollElasticityHelper::PinnedInDirection(
+    const gfx::Vector2dF& direction) {
+  gfx::ScrollOffset scroll_offset =
+      layer_tree_host_impl_->active_tree()->TotalScrollOffset();
+  gfx::ScrollOffset max_scroll_offset =
+      layer_tree_host_impl_->active_tree()->TotalMaxScrollOffset();
+  bool result = false;
+  if (direction.x() < 0)
+    result |= scroll_offset.x() <= 0;
+  if (direction.x() > 0)
+    result |= scroll_offset.x() >= max_scroll_offset.x();
+  if (direction.y() < 0)
+    result |= scroll_offset.y() <= 0;
+  if (direction.y() > 0)
+    result |= scroll_offset.y() >= max_scroll_offset.y();
+  return result;
+}
+
+bool ScrollElasticityHelper::CanScrollHorizontally() {
+  return layer_tree_host_impl_->active_tree()->TotalMaxScrollOffset().x() > 0;
+}
+
+bool ScrollElasticityHelper::CanScrollVertically() {
+  return layer_tree_host_impl_->active_tree()->TotalMaxScrollOffset().y() > 0;
+}
+
+gfx::Vector2dF ScrollElasticityHelper::AbsoluteScrollPosition() {
+  // TODO(ccameron): This is function is redundant and may be removed.
+  return stretch_offset_;
+}
+
+void ScrollElasticityHelper::ImmediateScrollBy(const gfx::Vector2dF& scroll) {
+  // TODO(ccameron): This is function is redundant and may be removed.
+}
+
+void ScrollElasticityHelper::ImmediateScrollByWithoutContentEdgeConstraints(
+    const gfx::Vector2dF& scroll) {
+  stretch_offset_ += scroll;
+
+  // TODO(ccameron): Update the transform of the appropriate layer in the
+  // LayerTreeHostImpl, and request that a frame be drawn.
+}
+
+void ScrollElasticityHelper::StartSnapRubberbandTimer() {
+  if (timer_active_)
+    return;
+  timer_active_ = true;
+  layer_tree_host_impl_->SetNeedsAnimate();
+}
+
+void ScrollElasticityHelper::StopSnapRubberbandTimer() {
+  timer_active_ = false;
+}
+
+void ScrollElasticityHelper::SnapRubberbandTimerFired() {
+  if (timer_active_)
+    layer_tree_host_impl_->SetNeedsAnimate();
+}
+
+void ScrollElasticityHelper::AdjustScrollPositionToBoundsIfNecessary() {
+  // TODO(ccameron): This is function is redundant and may be removed.
+}
+
+}  // namespace cc