Implement CSS: scroll-boundary-behavior

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 0b76c707c300350ea5cf56a1412fe38e4411144f..51e6965fd8dc85ebeae43b1d37c0e80b7fef42e7 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -80,7 +80,8 @@ LayerImpl::LayerImpl(LayerTreeImpl* tree_impl, int id)
       debug_info_(nullptr),
       has_will_change_transform_hint_(false),
       needs_push_properties_(false),
-      scrollbars_hidden_(false) {
+      scrollbars_hidden_(false),
+      scroll_boundary_behavior_(SCROLL_BOUNDARY_BEHAVIOR_PROPAGATE) {

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

How does a LayerImpl get scroll_boundary_behavior_ set? I think you need to add
a line in Layer::PushPropertiesTo(LayerImpl*)

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

Yeah, that's added.

[bokan, 2017/03/23 21:52:19]

Sorry, actually, now that you're storing the bit in ScrollNode, you don't
actually need to propagate this to LayerImpl. I think we can just return the
default value here and not worry about it, maybe DCHECK that it's not called?
+ajuma@, this value is only needed (and non-default from Blink) on cc::Layer to
build the scroll tree but the BuildPropertyTree functions demand both kinds of
layers have the same interface. What's the right way to handle this?

   DCHECK_GT(layer_id_, 0);
 
   DCHECK(layer_tree_impl_);
@@ -348,6 +349,7 @@ void LayerImpl::PushPropertiesTo(LayerImpl* layer) {
   layer->SetScrollClipLayer(scroll_clip_layer_id_);
   layer->SetElementId(element_id_);
   layer->SetMutableProperties(mutable_properties_);
+  layer->SetScrollBoundaryBehavior(scroll_boundary_behavior_);
 
   // If the main thread commits multiple times before the impl thread actually
   // draws, then damage tracking will become incorrect if we simply clobber the
@@ -834,6 +836,14 @@ gfx::Vector2dF LayerImpl::ClampScrollToMaxScrollOffset() {
   return delta;
 }
 
+void LayerImpl::SetScrollBoundaryBehavior(ScrollBoundaryBehavior behavior) {
+  if (scroll_boundary_behavior_ == behavior)
+    return;
+  scroll_boundary_behavior_ = behavior;
+  layer_tree_impl()->DidUpdateScrollState(id());
+  NoteLayerPropertyChanged();
+}
+
 void LayerImpl::SetNeedsPushProperties() {
   if (layer_tree_impl_ && !needs_push_properties_) {
     needs_push_properties_ = true;