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 613093e8041bef8ff4eaa4fe55d41e2a39de7da6..f79f47bdf085258bf53a319a915e99bc96d85178 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3012,6 +3012,7 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
       MainThreadScrollingReason::kNotScrollingOnMain;
   ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
+  bool x_dominated = (std::abs(scroll_delta.x()) > std::abs(scroll_delta.y()));
 
   if (scroll_node) {
     // Flash the overlay scrollbar even if the scroll dalta is 0.
@@ -3091,6 +3092,14 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
       }
 
       pending_delta -= scroll_delta;
+
+      if ((x_dominated &&
+           scroll_node->scroll_boundary_behavior.x !=
+               ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto) ||
+          (!x_dominated &&
+           scroll_node->scroll_boundary_behavior.y !=
+               ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto))
+        break;
     }
   }
   scroll_state.set_is_ending(true);
@@ -3298,6 +3307,8 @@ void LayerTreeHostImpl::DistributeScrollDelta(ScrollState* scroll_state) {
   ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
   ScrollNode* viewport_scroll_node = OuterViewportScrollNode();
+  bool x_dominated =
+      (std::abs(scroll_state->delta_x()) > std::abs(scroll_state->delta_y()));
   if (scroll_node) {
     // TODO(bokan): The loop checks for a null parent but don't we still want to
     // distribute to the root scroll node?
@@ -3312,10 +3323,16 @@ 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);
+      if ((x_dominated &&
+           scroll_node->scroll_boundary_behavior.x !=
+               ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto) ||
+          (!x_dominated &&
+           scroll_node->scroll_boundary_behavior.y !=
+               ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto))
+        break;
     }
   }
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,