Adding momentum/overscroll to views:: ScrollViews

cc/trees/draw_property_utils.cc

Index: cc/trees/draw_property_utils.cc
diff --git a/cc/trees/draw_property_utils.cc b/cc/trees/draw_property_utils.cc
index 366fafc6df72640bd27cca9bab90176a8eecf8d6..f3b2a2fcbec88ae17ffcc2744e34b40101a1cf26 100644
--- a/cc/trees/draw_property_utils.cc
+++ b/cc/trees/draw_property_utils.cc
@@ -1559,16 +1559,21 @@ static void UpdateElasticOverscrollInternal(
     const LayerType* overscroll_elasticity_layer,
     const gfx::Vector2dF& elastic_overscroll) {
   if (!overscroll_elasticity_layer) {
-    DCHECK(elastic_overscroll.IsZero());
+    // When only the viewport has elasticity, elastic_overscroll should be zero
+    // here, but for now elasticity doesn't bubble up, only down. So, that won't
+    // be the case if a sublayer has its own overscroll.
+    // TODO(tapted): Give the viewport overscroll and completely remove
+    // overscroll_elasticity_layer.
     return;
   }
 
   TransformNode* node = property_trees->transform_tree.Node(
       overscroll_elasticity_layer->transform_tree_index());
-  if (node->scroll_offset == gfx::ScrollOffset(elastic_overscroll))
+  if (node->scroll_offset_with_overscroll ==
+      gfx::ScrollOffset(elastic_overscroll))
     return;
 
-  node->scroll_offset = gfx::ScrollOffset(elastic_overscroll);
+  node->scroll_offset_with_overscroll = gfx::ScrollOffset(elastic_overscroll);
   node->needs_local_transform_update = true;
   property_trees->transform_tree.set_needs_update(true);
 }