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..fb476e7358e30c478bc54e6f65bfb426dd2e9115 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -2073,6 +2073,10 @@ void LayoutObject::mapLocalToAncestor(const LayoutBoxModelObject* ancestor,
   }
 
   LayoutSize containerOffset = offsetFromContainer(container);
+  if (isBoxModelObject() && isStickyPositioned() && (mode & IgnoreSticky)) {
+    containerOffset -= toLayoutBoxModelObject(this)->offsetForInFlowPosition();

[flackr, 2017/01/31 18:33:00]

It is a little unfortunate to calculate this offset twice though, maybe leave a
TODO to not include it in the above call to offsetFromContainer?

[smcgruer, 2017/01/31 20:42:16]

Done.

+  }
+
   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).