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 54dc7bbd336bc73f606cdad27254392eed83b148..f27e38a6f83d236116f3aa90d30313c21b552939 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3237,6 +3237,14 @@ void LayerTreeHostImpl::ApplyScroll(ScrollNode* scroll_node,
         scroll_node, delta, viewport_point,
         scroll_state->is_direct_manipulation(),
         &scroll_state->layer_tree_impl()->property_trees()->scroll_tree);
+    if (scroll_node->scroll_boundary_behavior.x !=

[bokan, 2017/05/19 19:35:57]

I believe you'll also need similar logic in LTHI::ScrollAnimated which is used
by smooth wheel scrolls and is a separate path from this.

[sunyunjia, 2017/05/25 20:07:10]

Done.

+            ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto &&
+        std::abs(delta.x()) > std::abs(delta.y()))
+      applied_delta.set_x(delta.x());
+    if (scroll_node->scroll_boundary_behavior.y !=
+            ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto &&
+        std::abs(delta.y()) > std::abs(delta.x()))
+      applied_delta.set_y(delta.y());

[bokan, 2017/05/19 19:35:57]

I think we should do this in DistributeScrollDelta where we calculate the scroll
chain.

[sunyunjia, 2017/05/25 20:07:10]

Done.

   }
 
   // If the layer wasn't able to move, try the next one in the hierarchy.
@@ -3298,10 +3306,8 @@ void LayerTreeHostImpl::DistributeScrollDelta(ScrollState* scroll_state) {
         break;
       }
 
-      if (!scroll_node->scrollable)
-        continue;
-
-      current_scroll_chain.push_front(scroll_node);
+      if (scroll_node->scrollable)
+        current_scroll_chain.push_front(scroll_node);
     }
   }
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,