Overscroll and Elasticity for views::ScrollView

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 517a1c6a634511b8774f01d285dcac06f1038d5d..73f5dae54fabd7a63b55933868768829a9eb889b 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -772,8 +772,10 @@ void Layer::SetScrollOffset(const gfx::ScrollOffset& scroll_offset) {
     return;
 
   PropertyTrees* property_trees = layer_tree_->property_trees();
-  if (scroll_tree_index() != ScrollTree::kInvalidNodeId && scrollable())
-    property_trees->scroll_tree.SetScrollOffset(id(), scroll_offset);
+  if (scroll_tree_index() != ScrollTree::kInvalidNodeId && scrollable()) {
+    property_trees->scroll_tree.SetScrollOffset(id(), inputs_.scroll_offset,
+                                                inputs_.overscroll);
+  }
 
   if (property_trees->IsInIdToIndexMap(PropertyTrees::TreeType::TRANSFORM,
                                        id())) {
@@ -781,7 +783,8 @@ void Layer::SetScrollOffset(const gfx::ScrollOffset& scroll_offset) {
               property_trees->transform_id_to_index_map[id()]);
     TransformNode* transform_node =
         property_trees->transform_tree.Node(transform_tree_index());
-    transform_node->scroll_offset = CurrentScrollOffset();
+    transform_node->scroll_offset_with_overscroll =
+        inputs_.scroll_offset + inputs_.overscroll;
     transform_node->needs_local_transform_update = true;
     property_trees->transform_tree.set_needs_update(true);
     SetNeedsCommitNoRebuild();
@@ -791,22 +794,33 @@ void Layer::SetScrollOffset(const gfx::ScrollOffset& scroll_offset) {
   SetNeedsCommit();
 }
 
-void Layer::SetScrollOffsetFromImplSide(
-    const gfx::ScrollOffset& scroll_offset) {
+void Layer::SetScrollOffsetFromImplSide(const gfx::ScrollOffset& scroll_offset,
+                                        gfx::Vector2dF* overscroll_delta) {
   DCHECK(IsPropertyChangeAllowed());
   // This function only gets called during a BeginMainFrame, so there
   // is no need to call SetNeedsUpdate here.
   DCHECK(layer_tree_host_ && layer_tree_host_->CommitRequested());
-  if (inputs_.scroll_offset == scroll_offset)
+
+  gfx::ScrollOffset overscroll = inputs_.overscroll;
+  if (inputs_.can_overscroll && overscroll_delta) {
+    overscroll = gfx::ScrollOffsetWithDelta(overscroll, *overscroll_delta);
+    *overscroll_delta = gfx::Vector2dF();
+  }
+  if (inputs_.scroll_offset == scroll_offset &&
+      inputs_.overscroll == overscroll)
     return;
+
   inputs_.scroll_offset = scroll_offset;
+  inputs_.overscroll = overscroll;
   SetNeedsPushProperties();
 
   bool needs_rebuild = true;
 
   PropertyTrees* property_trees = layer_tree_->property_trees();
-  if (scroll_tree_index() != ScrollTree::kInvalidNodeId && scrollable())
-    property_trees->scroll_tree.SetScrollOffset(id(), scroll_offset);
+  if (scroll_tree_index() != ScrollTree::kInvalidNodeId && scrollable()) {
+    property_trees->scroll_tree.SetScrollOffset(id(), inputs_.scroll_offset,
+                                                inputs_.overscroll);
+  }
 
   if (property_trees->IsInIdToIndexMap(PropertyTrees::TreeType::TRANSFORM,
                                        id())) {
@@ -814,7 +828,8 @@ void Layer::SetScrollOffsetFromImplSide(
               property_trees->transform_id_to_index_map[id()]);
     TransformNode* transform_node =
         property_trees->transform_tree.Node(transform_tree_index());
-    transform_node->scroll_offset = CurrentScrollOffset();
+    transform_node->scroll_offset_with_overscroll =
+        inputs_.scroll_offset + inputs_.overscroll;
     transform_node->needs_local_transform_update = true;
     property_trees->transform_tree.set_needs_update(true);
     needs_rebuild = false;
@@ -829,11 +844,14 @@ void Layer::SetScrollOffsetFromImplSide(
   // "this" may have been destroyed during the process.
 }
 
-void Layer::SetScrollClipLayerId(int clip_layer_id) {
+void Layer::SetScrollClipAndCanOverscroll(int clip_layer_id,
+                                          bool can_overscroll) {
   DCHECK(IsPropertyChangeAllowed());
-  if (inputs_.scroll_clip_layer_id == clip_layer_id)
+  if (inputs_.scroll_clip_layer_id == clip_layer_id &&
+      inputs_.can_overscroll == can_overscroll)
     return;
   inputs_.scroll_clip_layer_id = clip_layer_id;
+  inputs_.can_overscroll = can_overscroll;
   SetNeedsCommit();
 }
 
@@ -1165,7 +1183,8 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   layer->SetShouldCheckBackfaceVisibility(should_check_backface_visibility_);
   layer->Set3dSortingContextId(inputs_.sorting_context_id);
 
-  layer->SetScrollClipLayer(inputs_.scroll_clip_layer_id);
+  layer->SetScrollClipAndCanOverscroll(inputs_.scroll_clip_layer_id,
+                                       inputs_.can_overscroll);
   layer->set_user_scrollable_horizontal(inputs_.user_scrollable_horizontal);
   layer->set_user_scrollable_vertical(inputs_.user_scrollable_vertical);
   layer->SetElementId(inputs_.element_id);
@@ -1349,9 +1368,11 @@ void Layer::LayerSpecificPropertiesToProto(proto::LayerProperties* proto,
       inputs_.use_parent_backface_visibility);
   base->set_background_color(inputs_.background_color);
   ScrollOffsetToProto(inputs_.scroll_offset, base->mutable_scroll_offset());
+  ScrollOffsetToProto(inputs_.overscroll, base->mutable_overscroll());
   base->set_scroll_clip_layer_id(inputs_.scroll_clip_layer_id);
   base->set_user_scrollable_horizontal(inputs_.user_scrollable_horizontal);
   base->set_user_scrollable_vertical(inputs_.user_scrollable_vertical);
+  base->set_can_overscroll(inputs_.can_overscroll);
   base->set_main_thread_scrolling_reasons(
       inputs_.main_thread_scrolling_reasons);
   RegionToProto(inputs_.non_fast_scrollable_region,
@@ -1487,6 +1508,7 @@ void Layer::FromLayerSpecificPropertiesProto(
   inputs_.scroll_clip_layer_id = base.scroll_clip_layer_id();
   inputs_.user_scrollable_horizontal = base.user_scrollable_horizontal();
   inputs_.user_scrollable_vertical = base.user_scrollable_vertical();
+  inputs_.can_overscroll = base.can_overscroll();
 
   inputs_.scroll_parent = base.scroll_parent_id() == INVALID_ID
                               ? nullptr
@@ -1527,6 +1549,7 @@ void Layer::FromLayerSpecificPropertiesProto(
   }
 
   inputs_.scroll_offset = ProtoToScrollOffset(base.scroll_offset());
+  inputs_.overscroll = ProtoToScrollOffset(base.overscroll());
 
   inputs_.update_rect.Union(ProtoToRect(base.update_rect()));