Overscroll and Elasticity for views::ScrollView

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 761b1df837f9d28eac2d180ecd3e745abd5cb4c5..3c4f948f4cb0a1645fa2240bfc8662f913903682 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -57,6 +57,7 @@ LayerImpl::LayerImpl(LayerTreeImpl* tree_impl, int id)
           MainThreadScrollingReason::kNotScrollingOnMain),
       user_scrollable_horizontal_(true),
       user_scrollable_vertical_(true),
+      can_overscroll_(false),
       should_flatten_transform_from_property_tree_(false),
       layer_property_changed_(false),
       may_contain_video_(false),
@@ -287,12 +288,15 @@ gfx::Vector2dF LayerImpl::ScrollBy(const gfx::Vector2dF& scroll) {
   return scroll_tree.ScrollBy(scroll_node, scroll, layer_tree_impl());
 }
 
-void LayerImpl::SetScrollClipLayer(int scroll_clip_layer_id) {
-  if (scroll_clip_layer_id_ == scroll_clip_layer_id)
+void LayerImpl::SetScrollClipAndCanOverscroll(int scroll_clip_layer_id,
+                                              bool can_overscroll) {
+  if (scroll_clip_layer_id_ == scroll_clip_layer_id &&
+      can_overscroll_ == can_overscroll)
     return;
 
   layer_tree_impl()->UnregisterScrollLayer(this);
   scroll_clip_layer_id_ = scroll_clip_layer_id;
+  can_overscroll_ = can_overscroll;
   layer_tree_impl()->RegisterScrollLayer(this);
 }
 
@@ -368,7 +372,7 @@ void LayerImpl::PushPropertiesTo(LayerImpl* layer) {
   if (layer->has_render_surface() != has_render_surface())
     layer->layer_tree_impl()->set_needs_update_draw_properties();
   layer->SetBounds(bounds_);
-  layer->SetScrollClipLayer(scroll_clip_layer_id_);
+  layer->SetScrollClipAndCanOverscroll(scroll_clip_layer_id_, can_overscroll_);
   layer->SetElementId(element_id_);
   layer->SetMutableProperties(mutable_properties_);
 
@@ -833,8 +837,8 @@ void LayerImpl::AddDamageRect(const gfx::Rect& damage_rect) {
 
 void LayerImpl::SetCurrentScrollOffset(const gfx::ScrollOffset& scroll_offset) {
   DCHECK(IsActive());
-  if (layer_tree_impl()->property_trees()->scroll_tree.SetScrollOffset(
-          id(), scroll_offset))
+  ScrollTree& scroll_tree = layer_tree_impl()->property_trees()->scroll_tree;
+  if (scroll_tree.SetScrollOffset(id(), scroll_offset, CurrentOverscroll()))
     layer_tree_impl()->DidUpdateScrollOffset(id());
 }
 
@@ -843,15 +847,27 @@ gfx::ScrollOffset LayerImpl::CurrentScrollOffset() const {
       id());
 }
 
+void LayerImpl::SetCurrentOverscroll(const gfx::ScrollOffset& overscroll) {
+  ScrollTree& scroll_tree = layer_tree_impl()->property_trees()->scroll_tree;
+  if (scroll_tree.SetScrollOffset(id(), CurrentScrollOffset(), overscroll))
+    layer_tree_impl()->DidUpdateScrollOffset(id());
+}
+
+gfx::ScrollOffset LayerImpl::CurrentOverscroll() const {
+  return layer_tree_impl()->property_trees()->scroll_tree.current_overscroll(
+      id());
+}
+
 void LayerImpl::UpdatePropertyTreeScrollOffset() {
   // TODO(enne): in the future, scrolling should update the scroll tree
   // directly instead of going through layers.
   TransformTree& transform_tree =
       layer_tree_impl()->property_trees()->transform_tree;
   TransformNode* node = transform_tree.Node(transform_tree_index_);
-  gfx::ScrollOffset current_offset = CurrentScrollOffset();
-  if (node->scroll_offset != current_offset) {
-    node->scroll_offset = current_offset;
+  gfx::ScrollOffset current_offset =
+      CurrentScrollOffset() + CurrentOverscroll();
+  if (node->scroll_offset_with_overscroll != current_offset) {
+    node->scroll_offset_with_overscroll = current_offset;
     node->needs_local_transform_update = true;
     transform_tree.set_needs_update(true);
   }