Implement closed shadow adjustment for Element.offsetParent

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

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index d538266bd94ed7898d2cb0069bc7f77942136a9a..6cfd04ecf988d45be7590c9ad215c656403d8390 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -663,6 +663,7 @@ public:
     bool isInFlowPositioned() const { return m_bitfields.isInFlowPositioned(); } // relative or sticky positioning
     bool isRelPositioned() const { return m_bitfields.isRelPositioned(); } // relative positioning
     bool isStickyPositioned() const { return m_bitfields.isStickyPositioned(); } // sticky positioning
+    bool isFixedPositioned() const { return isOutOfFlowPositioned() && style()->position() == FixedPosition; } // fixed positioning
     bool isPositioned() const { return m_bitfields.isPositioned(); }
 
     bool isText() const  { return m_bitfields.isText(); }
@@ -815,7 +816,7 @@ public:
 
     virtual LayoutObject* hoverAncestor() const { return parent(); }
 
-    Element* offsetParent() const;
+    Element* offsetParent(const Element* = nullptr) const;
 
     void markContainerChainForLayout(bool scheduleRelayout = true, SubtreeLayoutScope* = nullptr);
     void setNeedsLayout(LayoutInvalidationReasonForTracing, MarkingBehavior = MarkContainerChain, SubtreeLayoutScope* = nullptr);