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

Source/core/layout/TracedLayoutObject.cpp

Index: Source/core/layout/TracedLayoutObject.cpp
diff --git a/Source/core/layout/TracedLayoutObject.cpp b/Source/core/layout/TracedLayoutObject.cpp
index 586e234b195e25efe1ab10adc3a99fb0ff12b761..68f5281b12a3a960c08690bfdbd5d7605bf8c6d5 100644
--- a/Source/core/layout/TracedLayoutObject.cpp
+++ b/Source/core/layout/TracedLayoutObject.cpp
@@ -31,6 +31,7 @@ TracedLayoutObject::TracedLayoutObject(const LayoutObject& object)
     , m_isAnonymous(object.isAnonymous())
     , m_isPositioned(object.isOutOfFlowPositioned())
     , m_isRelPositioned(object.isRelPositioned())
+    , m_isStickyPositioned(object.isStickyPositioned())
     , m_isFloating(object.isFloating())
     , m_selfNeeds(object.selfNeedsLayout())
     , m_positionedMovement(object.needsPositionedMovementLayout())
@@ -125,6 +126,8 @@ PassRefPtr<JSONObject> TracedLayoutObject::toJSON() const
         json->setBoolean("anonymous", m_isAnonymous);
     if (m_isRelPositioned)
         json->setBoolean("relativePositioned", m_isRelPositioned);
+    if (m_isStickyPositioned)
+        json->setBoolean("stickyPositioned", m_isStickyPositioned);
     if (m_isFloating)
         json->setBoolean("float", m_isFloating);
     if (m_children.size()) {