Conditionally create PaintLayer's scrollable area object

third_party/WebKit/Source/core/paint/PaintLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 722 matching lines @@
 
     bool shouldBeSelfPaintingLayer() const;
 
     // FIXME: We should only create the stacking node if needed.
     bool requiresStackingNode() const { return true; }
     void updateStackingNode();
 
     void updateReflectionInfo(const ComputedStyle*);
     FilterEffectBuilder* updateFilterEffectBuilder() const;
 
-    // FIXME: We could lazily allocate our ScrollableArea based on style properties ('overflow', ...)
-    // but for now, we are always allocating it for LayoutBox as it's safer. crbug.com/467721.
-    bool requiresScrollableArea() const { return layoutBox(); }
+    bool requiresScrollableArea() const { return m_layoutObject->hasOverflowClip() || m_layoutObject->isLayoutView() || m_layoutObject->styleRef().resize() != RESIZE_NONE; }
     void updateScrollableArea();
 
     void dirtyAncestorChainVisibleDescendantStatus();
 
     bool attemptDirectCompositingUpdate(StyleDifference, const ComputedStyle* oldStyle);
     void updateTransform(const ComputedStyle* oldStyle, const ComputedStyle& newStyle);
 
     void dirty3DTransformedDescendantStatus();
     // Both updates the status, and returns true if descendants of this have 3d.
     bool update3DTransformedDescendantStatus();
@@ skipping 114 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const blink::PaintLayer*);
 void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif // Layer_h