RLSA needsLayout on customscrollbar thickness change.

Source/core/rendering/RenderBlock.cpp

 /*
  * 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, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. 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
@@ skipping 1369 matching lines @@
     }
 }
 
 void RenderBlock::layout()
 {
     OverflowEventDispatcher dispatcher(this);
 
     // Update our first letter info now.
     updateFirstLetter();
 
+    bool relayoutChildren = false;
+
+    // If CustomScrollbar Rect is changed, RenderBlock and child needs reLayout.
+    if (hasOverflowClip())
+        relayoutChildren |= layer()->scrollableArea()->didCustomScrollbarRectChanged();

[skobes, 2014/11/13 18:14:26]

RenderBlockFlow::layoutBlockFlow has logic to force relayout of children when
the block's width has changed.  I guess the logicalWidth() includes scrollbars,
so it doesn't change when the scrollbar width changes, therefore we don't
relayout the children when we should?  If that's the root cause then the best
place for the fix might be in RenderBlock::widthAvailableToChildrenHasChanged().

In that case I would try to use m_hasBorderOrPaddingLogicalWidthChanged to track
it, instead of adding state to RenderLayerScrollableArea.  You can rename the
field m_widthAvailableToChildrenChanged since it is affected by more than just
border or padding changes.

[MuVen, 2014/11/13 20:34:10]

I have added a variable in the RenderBox to inform customscrollbar thickness
changed, as change in RenderScrollbarPart width will not trigger
widthAvailableToChildrenHasChanged.

+
     // Table cells call layoutBlock directly, so don't add any logic here.  Put code into
     // layoutBlock().
-    layoutBlock(false);
+    layoutBlock(relayoutChildren);
 
     // It's safe to check for control clip here, since controls can never be table cells.
     // If we have a lightweight clip, there can never be any overflow from children.
     if (hasControlClip() && m_overflow)
         clearLayoutOverflow();
 
     invalidateBackgroundObscurationStatus();
 }
 
 bool RenderBlock::updateImageLoadingPriorities()
@@ skipping 3007 matching lines @@
 void RenderBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const RenderObject* obj) const
 {
     showRenderObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace blink