Add overflow:auto scrollbars to child flex basis.

Source/core/paint/DeprecatedPaintLayerScrollableArea.h

Index: Source/core/paint/DeprecatedPaintLayerScrollableArea.h
diff --git a/Source/core/paint/DeprecatedPaintLayerScrollableArea.h b/Source/core/paint/DeprecatedPaintLayerScrollableArea.h
index ebc66fe275a337d64ccfa694c013ad732f32e5e1..c7b2756f8cfd8ba57716c3328f8f05e0277ffb08 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.h
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.h
@@ -149,6 +149,9 @@ public:
         scrollToOffset(toDoubleSize(position), ScrollOffsetClamped, scrollBehavior);
     }
 
+    void updateScrollDimensions(DoubleSize& scrollOffset, bool& autoHorizontalScrollBarChanged, bool& autoVerticalScrollBarChanged);
+    void finalizeScrollDimensions(const DoubleSize& originalScrollOffset, bool autoHorizontalScrollBarChanged, bool autoVerticalScrollBarChanged);
+
     void updateAfterLayout();
     void updateAfterStyleChange(const ComputedStyle*);
     void updateAfterOverflowRecalc();