Revert changes is the use of CompositingReasonOutOfFlowClipping

third_party/WebKit/Source/core/layout/compositing/CompositingReasonFinder.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 "core/layout/compositing/CompositingReasonFinder.h"
 
 #include "core/CSSPropertyNames.h"
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
@@ skipping 125 matching lines @@
   // but the layoutObject may be an inline that doesn't support them.
   return layoutObject->hasTransformRelatedProperty() &&
          layoutObject->style()->has3DTransform();
 }
 
 CompositingReasons CompositingReasonFinder::nonStyleDeterminedDirectReasons(
     const PaintLayer* layer) const {
   CompositingReasons directReasons = CompositingReasonNone;
   LayoutObject* layoutObject = layer->layoutObject();
 
-  if (layer->needsCompositedScrolling())
+  bool checkForClipParent =
+      (m_compositingTriggers & OverflowScrollTrigger) &&
+      layer->ancestorScrollingLayer() &&
+      layer->ancestorScrollingLayer()->compositingState() ==
+          PaintsIntoOwnBacking;
+  if (layer->needsCompositedScrolling()) {
+    checkForClipParent = true;
     directReasons |= CompositingReasonOverflowScrollingTouch;
+  }
+  if (checkForClipParent && layer->clipParent())
+    directReasons |= CompositingReasonOutOfFlowClipping;
 
   // Composite |layer| if it is inside of an ancestor scrolling layer, but that
   // scrolling layer is not on the stacking context ancestor chain of |layer|.
   // See the definition of the scrollParent property in Layer for more detail.
   if (const PaintLayer* scrollingAncestor = layer->ancestorScrollingLayer()) {
     if (scrollingAncestor->needsCompositedScrolling() && layer->scrollParent())
       directReasons |= CompositingReasonOverflowScrollingParent;
   }
 
   // TODO(flackr): Rename functions and variables to include sticky position (i.e. ScrollDependentPosition rather than PositionFixed).
@@ skipping 28 matching lines @@
   }
   // Don't promote fixed position elements that are descendants of a non-view container, e.g. transformed elements.
   // They will stay fixed wrt the container rather than the enclosing frame.
   if (layer->scrollsWithViewport())
     return m_layoutView.frameView()->isScrollable();
   return layer->layoutObject()->style()->position() == StickyPosition &&
          layer->ancestorOverflowLayer()->scrollsOverflow();
 }
 
 }  // namespace blink