Reconstruct customscrollbars if owningLayoutObject changes.

Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp

Index: Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
index 2bfbb871ad730bfe8fd927c5349c3393d086f9a6..20d066b5ad6ebb11f93eddb9af39e5c41452688f 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
@@ -966,7 +966,7 @@ static inline LayoutObject* layoutObjectForScrollbar(LayoutObject& layoutObject)
             // If we have an owning ipage/LocalFrame element, then it can set the custom scrollbar also.
             LayoutPart* frameLayoutObject = node->document().frame()->ownerLayoutObject();
             if (frameLayoutObject && frameLayoutObject->style()->hasPseudoStyle(SCROLLBAR))
-                return frameLayoutObject;
+                return &layoutObject;

[skobes, 2015/09/12 02:36:52]

Based on the comment on line 966, it looks like the intent of this code is to
use the styles applied to the <iframe> element to draw the scrollbars inside the
iframe.  Won't this break that logic?

         }
         if (ShadowRoot* shadowRoot = node->containingShadowRoot()) {
             if (shadowRoot->type() == ShadowRootType::UserAgent)