RLSA needsLayout on customscrollbar thickness change.

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index 01828a11a386acf151a0fd570b615d77a67acf45..f87f190bc92b6a32b9e044368b5a7d18834b4da9 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -1387,9 +1387,15 @@ void RenderBlock::layout()
     // 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.