Update from https://crrev.com/309717

cc/input/scroll_elasticity_helper.cc

Index: cc/input/scroll_elasticity_helper.cc
diff --git a/cc/input/scroll_elasticity_helper.cc b/cc/input/scroll_elasticity_helper.cc
index 7065e86a4911e236cecbf1912d9e87bd53cbc037..1e9fe7dff9f59fd482a286d89fc8dc5a613ac2aa 100644
--- a/cc/input/scroll_elasticity_helper.cc
+++ b/cc/input/scroll_elasticity_helper.cc
@@ -13,15 +13,13 @@ namespace cc {
 class ScrollElasticityHelperImpl : public ScrollElasticityHelper {
  public:
   explicit ScrollElasticityHelperImpl(LayerTreeHostImpl* layer_tree_host_impl);
-  virtual ~ScrollElasticityHelperImpl();
+  ~ScrollElasticityHelperImpl() override;
 
-  // The amount that the view is stretched past the normal allowable bounds.
-  // The "overhang" amount.
-  gfx::Vector2dF StretchAmount() override;
+  gfx::Vector2dF StretchAmount() const override;
   void SetStretchAmount(const gfx::Vector2dF& stretch_amount) override;
-  bool PinnedInDirection(const gfx::Vector2dF& direction) override;
-  bool CanScrollHorizontally() override;
-  bool CanScrollVertically() override;
+  gfx::ScrollOffset ScrollOffset() const override;
+  gfx::ScrollOffset MaxScrollOffset() const override;
+  void ScrollBy(const gfx::Vector2dF& delta) override;
   void RequestAnimate() override;
 
  private:
@@ -36,8 +34,8 @@ ScrollElasticityHelperImpl::ScrollElasticityHelperImpl(
 ScrollElasticityHelperImpl::~ScrollElasticityHelperImpl() {
 }
 
-gfx::Vector2dF ScrollElasticityHelperImpl::StretchAmount() {
-  return -layer_tree_host_impl_->active_tree()->elastic_overscroll()->Current(
+gfx::Vector2dF ScrollElasticityHelperImpl::StretchAmount() const {
+  return layer_tree_host_impl_->active_tree()->elastic_overscroll()->Current(
       true);
 }
 
@@ -47,37 +45,28 @@ void ScrollElasticityHelperImpl::SetStretchAmount(
     return;
 
   layer_tree_host_impl_->active_tree()->elastic_overscroll()->SetCurrent(
-      -stretch_amount);
+      stretch_amount);
   layer_tree_host_impl_->active_tree()->set_needs_update_draw_properties();
   layer_tree_host_impl_->SetNeedsCommit();
   layer_tree_host_impl_->SetNeedsRedraw();
   layer_tree_host_impl_->SetFullRootLayerDamage();
 }
 
-bool ScrollElasticityHelperImpl::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;
+gfx::ScrollOffset ScrollElasticityHelperImpl::ScrollOffset() const {
+  return layer_tree_host_impl_->active_tree()->TotalScrollOffset();
 }
 
-bool ScrollElasticityHelperImpl::CanScrollHorizontally() {
-  return layer_tree_host_impl_->active_tree()->TotalMaxScrollOffset().x() > 0;
+gfx::ScrollOffset ScrollElasticityHelperImpl::MaxScrollOffset() const {
+  return layer_tree_host_impl_->active_tree()->TotalMaxScrollOffset();
 }
 
-bool ScrollElasticityHelperImpl::CanScrollVertically() {
-  return layer_tree_host_impl_->active_tree()->TotalMaxScrollOffset().y() > 0;
+void ScrollElasticityHelperImpl::ScrollBy(const gfx::Vector2dF& delta) {
+  LayerImpl* root_scroll_layer =
+      layer_tree_host_impl_->OuterViewportScrollLayer()
+          ? layer_tree_host_impl_->OuterViewportScrollLayer()
+          : layer_tree_host_impl_->InnerViewportScrollLayer();
+  if (root_scroll_layer)
+    root_scroll_layer->ScrollBy(delta);
 }
 
 void ScrollElasticityHelperImpl::RequestAnimate() {