Adapt and reland old position sticky implementation

Source/platform/graphics/CompositingReasons.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/graphics/CompositingReasons.h"
 
 #include "wtf/StdLibExtras.h"
 
 namespace blink {
@@ skipping 22 matching lines @@
         "Has backface-visibility: hidden" },
     { CompositingReasonActiveAnimation,
         "activeAnimation",
         "Has an active accelerated animation or transition" },
     { CompositingReasonTransitionProperty,
         "transitionProperty",
         "Has an acceleratable transition property (active or inactive)" },
     { CompositingReasonPositionFixed,
         "positionFixed",
         "Is fixed position" },
+    { CompositingReasonPositionSticky,
+        "positionSticky",
+        "Is sticky position" },
     { CompositingReasonOverflowScrollingTouch,
         "overflowScrollingTouch",
         "Is a scrollable overflow element" },
     { CompositingReasonOverflowScrollingParent,
         "overflowScrollingParent",
         "Scroll parent is not an ancestor" },
     { CompositingReasonOutOfFlowClipping,
         "outOfFlowClipping",
         "Has clipping ancestor" },
     { CompositingReasonVideoOverlay,
@@ skipping 144 matching lines @@
         "layerForScrollingBlockSelection",
         "Secondary layer, to house block selection gaps for composited scrolling with no scrolling contents" },
     { CompositingReasonInlineTransform,
         "inlineTransform",
         "Has an inline transform, which causes subsequent layers to assume overlap" },
 };
 
 size_t kNumberOfCompositingReasons = WTF_ARRAY_LENGTH(kCompositingReasonStringMap);
 
 } // namespace blink