Reconstruct customscrollbars if owningLayoutObject changes.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 87dd24a0fc8f655055b21fc360ebbc36a5a4dcf9..843ced35694e7bb2c25b9425be2407ebccf13e07 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1016,7 +1016,19 @@ bool PaintLayerScrollableArea::needsScrollbarReconstruction() const
     bool shouldUseCustom = actualLayoutObject.isBox() && actualLayoutObject.styleRef().hasPseudoStyle(SCROLLBAR);
     bool hasAnyScrollbar = hasScrollbar();
     bool hasCustom = (hasHorizontalScrollbar() && horizontalScrollbar()->isCustomScrollbar()) || (hasVerticalScrollbar() && verticalScrollbar()->isCustomScrollbar());
-    return hasAnyScrollbar && (shouldUseCustom != hasCustom);
+    bool didCustomScrollbarOwnerChanged = false;
+
+    if (hasHorizontalScrollbar() && horizontalScrollbar()->isCustomScrollbar()) {
+        if (actualLayoutObject != toLayoutScrollbar(horizontalScrollbar())->owningLayoutObject())
+            didCustomScrollbarOwnerChanged = true;
+    }
+
+    if (hasVerticalScrollbar() && verticalScrollbar()->isCustomScrollbar()) {
+        if (actualLayoutObject != toLayoutScrollbar(verticalScrollbar())->owningLayoutObject())
+            didCustomScrollbarOwnerChanged = true;
+    }
+
+    return hasAnyScrollbar && ((shouldUseCustom != hasCustom) || (shouldUseCustom && didCustomScrollbarOwnerChanged));
 }
 
 void PaintLayerScrollableArea::setHasHorizontalScrollbar(bool hasScrollbar)