Implement CSS: scroll-boundary-behavior

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index d9f1a22aefd1c60effdaa1f527280a69a8ceda65..0420b918518830d6b33dc4250dbf9ddf48ab3ddc 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3171,10 +3171,13 @@ void LayerTreeHostImpl::DistributeScrollDelta(ScrollState* scroll_state) {
         break;
       }
 
-      if (!scroll_node->scrollable)
-        continue;
+      if (scroll_node->scrollable)
+        current_scroll_chain.push_front(scroll_node);
 
-      current_scroll_chain.push_front(scroll_node);
+      LayerImpl* layer =

[bokan, 2017/03/23 13:18:26]

Layers are eventually going away. Instead of propagating the boundary behavior
to the LayerImpl, you should set it directly on the ScrollNode in
PropertyTreeBuilder. See AddScrollNodeIfNeeded in property_tree_builder.cc. You
may need to keep a method in LayerImpl to match the one in Layer since the
function is generic for layer types but it doesn't need to do anything since the
boundary behavior will always come from cc::Layer only.

[sunyunjia, 2017/03/23 20:16:54]

Done.

+          active_tree()->FindActiveTreeLayerById(scroll_node->owning_layer_id);
+      if (layer->scrollBoundaryBehavior() != SCROLL_BOUNDARY_BEHAVIOR_PROPAGATE)
+        break;
     }
   }
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,