Handle nested position:sticky elements

third_party/WebKit/Source/core/layout/LayoutObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index 1bb5c34bf25a12f7bdcc9c3425b855fe1d446c5f..ce671c30483a43332c6d8515cf72df8b4f501927 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -2072,7 +2072,8 @@ void LayoutObject::mapLocalToAncestor(const LayoutBoxModelObject* ancestor,
     }
   }
 
-  LayoutSize containerOffset = offsetFromContainer(container);
+  LayoutSize containerOffset =
+      offsetFromContainer(container, mode & IgnoreSticky);

[flackr, 2017/01/31 00:20:33]

I think this might be cleaner if we add staticOffsetFromContainer which excludes
the in flow positioning (and called from offsetFromContainer) or if you just
directly remove offsetForInFlowPosition here if the element is sticky and
ignoresticky is set. Adding arguments to offsetFromContainer feels a bit hacky.

[smcgruer, 2017/01/31 16:07:06]

I've gone for the direct removal for now. It's not pretty, but when I tried to
do the staticOffsetFromContainer implementation I ran into layout test failures
I didnt understand, so leaving the ugliness in for now :).

   if (isLayoutFlowThread()) {
     // So far the point has been in flow thread coordinates (i.e. as if
     // everything in the fragmentation context lived in one tall single column).
@@ -2306,7 +2307,8 @@ TransformationMatrix LayoutObject::localToAncestorTransform(
   return transformState.accumulatedTransform();
 }
 
-LayoutSize LayoutObject::offsetFromContainer(const LayoutObject* o) const {
+LayoutSize LayoutObject::offsetFromContainer(const LayoutObject* o,
+                                             bool ignoreSticky) const {
   ASSERT(o == container());
   return o->hasOverflowClip()
              ? LayoutSize(-toLayoutBox(o)->scrolledContentOffset())