Implement CSS: scroll-boundary-behavior

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 3153 matching lines @@
          scroll_node = scroll_tree.parent(scroll_node)) {
       if (scroll_node == viewport_scroll_node) {
         // Don't chain scrolls past the outer viewport scroll layer. Once we
         // reach that, we should scroll the viewport which is represented by the
         // main viewport scroll layer.
         DCHECK(viewport_scroll_node);
         current_scroll_chain.push_front(viewport_scroll_node);
         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,
                                                 active_tree());
   scroll_state->DistributeToScrollChainDescendant();
 }
 
 InputHandlerScrollResult LayerTreeHostImpl::ScrollBy(
     ScrollState* scroll_state) {
   DCHECK(scroll_state);
@@ skipping 998 matching lines @@
       worker_context_visibility_ =
           worker_context->CacheController()->ClientBecameVisible();
     } else {
       worker_context->CacheController()->ClientBecameNotVisible(
           std::move(worker_context_visibility_));
     }
   }
 }
 
 }  // namespace cc