Before finalizing scroll dimensions, check again whether we need scrollbars

third_party/WebKit/Source/core/layout/LayoutBlock.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 846 matching lines @@
     if (gDelayUpdateScrollInfo == 0) {
         ASSERT(gDelayedUpdateScrollInfoMap);
 
         OwnPtr<DelayedUpdateScrollInfoMap> infoMap(adoptPtr(gDelayedUpdateScrollInfoMap));
         gDelayedUpdateScrollInfoMap = nullptr;
 
         for (auto block : *infoMap) {
             if (block.key->hasOverflowClip()) {
                 PaintLayerScrollableArea* scrollableArea = block.key->layer()->scrollableArea();
                 ScrollInfo& scrollInfo = block.value;
-                scrollableArea->finalizeScrollDimensions(scrollInfo.scrollOffset, scrollInfo.autoHorizontalScrollBarChanged, scrollInfo.autoVerticalScrollBarChanged);
+                bool autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged;

[szager1, 2015/12/15 21:43:30]

I don't think you want new bool's here.  Instead:

scrollableArea->updateScrollDimensions(scrollInfo.scrollOffset,
scrollInfo.autoHorizontalScrollbarChanged,
scrollInfo.autoVerticalScrollbarChanged);

The logic in updateScrollDimensions should do the right thing with the bool's.

+                scrollableArea->updateScrollDimensions(scrollInfo.scrollOffset, autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
+                scrollableArea->finalizeScrollDimensions(scrollInfo.scrollOffset, autoHorizontalScrollBarChanged || scrollInfo.autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged || scrollInfo.autoVerticalScrollBarChanged);
             }
         }
     }
 }
 
 void LayoutBlock::updateScrollInfoAfterLayout()
 {
     if (hasOverflowClip()) {
         if (style()->isFlippedBlocksWritingMode()) {
             // FIXME: https://bugs.webkit.org/show_bug.cgi?id=97937
@@ skipping 2033 matching lines @@
 void LayoutBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const LayoutObject* obj) const
 {
     showLayoutObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace blink