Enable position:sticky for <thead> and <tr> elements

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

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
index b14965cd8942153e182585d74d747d5b054ab45a..6488bb360cb8499efb3e8b20add03621c600852d 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
@@ -33,6 +33,7 @@
 #include "core/layout/LayoutFlexibleBox.h"
 #include "core/layout/LayoutGeometryMap.h"
 #include "core/layout/LayoutInline.h"
+#include "core/layout/LayoutTableCell.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
@@ -988,10 +989,19 @@ void LayoutBoxModelObject::UpdateStickyPositionConstraints() const {
   // nested position:sticky elements between themselves and their
   // containingBlock, and between the containingBlock and their scrollAncestor.
   //
-  // The respective search ranges are [container, containingBlock) and
+  // The respective search ranges are [locationContainer, containingBlock) and
   // [containingBlock, scrollAncestor).
+
+  // Table cells are a special case; Blink ignores them for locationContainer()
+  // purposes, but their sticky offset does affect descendant sticky objects.
+  // TODO(smcgruer): Remove cell override once Blink supports the correct
+  // locationContainer for CSS 3.
+  LayoutObject* location_container_for_sticky =
+      IsTableCell() ? ToLayoutTableCell(this)->Row() : location_container;
+
   constraints.SetNearestStickyBoxShiftingStickyBox(
-      FindFirstStickyBetween(location_container, containing_block));
+      FindFirstStickyBetween(location_container_for_sticky, containing_block));
+
   // We cannot use |scrollAncestor| here as it disregards the root
   // ancestorOverflowLayer(), which we should include.
   constraints.SetNearestStickyBoxShiftingContainingBlock(FindFirstStickyBetween(