Conditionally create PaintLayer's scrollable area object

third_party/WebKit/Source/core/layout/LayoutBlock.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 327 matching lines @@
     // descendant. If multiple calls are made to startDelayUpdateScrollInfo(),
     // finishDelayUpdateScrollInfo() will do nothing until finishDelayUpdateScrollInfo()
     // is called the same number of times.
     static void startDelayUpdateScrollInfo();
     static void finishDelayUpdateScrollInfo();
 
     void updateScrollInfoAfterLayout();
 
     void styleWillChange(StyleDifference, const ComputedStyle& newStyle) override;
     void styleDidChange(StyleDifference, const ComputedStyle* oldStyle) override;
+    void updateFromStyle() override;
+
+    virtual bool allowsOverflowClip() const;

[chrishtr, 2016/02/26 19:42:17]

Document this.

[Xianzhu, 2016/02/26 20:12:57]

Done.

 
     virtual bool hasLineIfEmpty() const;
 
     bool simplifiedLayout();
     virtual void simplifiedNormalFlowLayout();
 
 public:
     virtual void computeOverflow(LayoutUnit oldClientAfterEdge, bool = false);
 protected:
     virtual void addOverflowFromChildren();
@@ skipping 143 matching lines @@
     // FIXME: This is temporary as we move code that accesses block flow
     // member variables out of LayoutBlock and into LayoutBlockFlow.
     friend class LayoutBlockFlow;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBlock, isLayoutBlock());
 
 } // namespace blink
 
 #endif // LayoutBlock_h