Add position: sticky as supported position value when CSSStickyPosition is enabled.

Source/core/layout/LayoutBoxModelObject.cpp

Index: Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/Source/core/layout/LayoutBoxModelObject.cpp b/Source/core/layout/LayoutBoxModelObject.cpp
index 0ede20bb48886f0899303a9591bdc06d1a5b0dd6..3d860fe2ad2f28b8cf9d1b77a8d6d1e49b302486 100644
--- a/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/Source/core/layout/LayoutBoxModelObject.cpp
@@ -424,12 +424,12 @@ void LayoutBoxModelObject::updateFromStyle()
 
 static LayoutSize accumulateInFlowPositionOffsets(const LayoutObject* child)
 {
-    if (!child->isAnonymousBlock() || !child->isRelPositioned())
+    if (!child->isAnonymousBlock() || !child->isInFlowPositioned())
         return LayoutSize();
     LayoutSize offset;
     LayoutObject* p = toLayoutBlock(child)->inlineElementContinuation();
     while (p && p->isLayoutInline()) {
-        if (p->isRelPositioned()) {
+        if (p->isInFlowPositioned()) {
             LayoutInline* layoutInline = toLayoutInline(p);
             offset += layoutInline->offsetForInFlowPosition();
         }
@@ -546,7 +546,7 @@ LayoutPoint LayoutBoxModelObject::adjustedPositionRelativeToOffsetParent(const L
         if (offsetParent->isBox() && !offsetParent->isBody())
             referencePoint.move(-toLayoutBox(offsetParent)->borderLeft(), -toLayoutBox(offsetParent)->borderTop());
         if (!isOutOfFlowPositioned() || flowThreadContainingBlock()) {
-            if (isRelPositioned())
+            if (isInFlowPositioned())
                 referencePoint.move(relativePositionOffset());
 
             LayoutObject* current;