Add overflow:auto scrollbars to child flex basis.

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 75b2999646e092109c931114f7a27add34ba4c50..96514a631ad091cd0422521c64b1855b150cec43 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
@@ -642,12 +642,35 @@ void DeprecatedPaintLayerScrollableArea::scrollToOffset(const DoubleSize& scroll
     }
 }
 
-void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
+void DeprecatedPaintLayerScrollableArea::updateScrollDimensions(DoubleSize& scrollOffset, bool& autoHorizontalScrollBarChanged, bool& autoVerticalScrollBarChanged)
 {
     ASSERT(box().hasOverflowClip());
 
-    DoubleSize originalScrollOffset = adjustedScrollOffset();
+    scrollOffset = adjustedScrollOffset();
     computeScrollDimensions();
+    bool hasHorizontalOverflow = this->hasHorizontalOverflow();
+    bool hasVerticalOverflow = this->hasVerticalOverflow();
+    if (hasOverlayScrollbars()) {
+        if (!scrollSize(HorizontalScrollbar))
+            setHasHorizontalScrollbar(false);
+        if (!scrollSize(VerticalScrollbar))
+            setHasVerticalScrollbar(false);
+    }
+
+    // overflow:auto may need to lay out again if scrollbars got added/removed.
+    autoHorizontalScrollBarChanged = box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
+    autoVerticalScrollBarChanged = box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
+    if (!visualViewportSuppliesScrollbars() && (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged)) {
+        if (box().hasAutoHorizontalScrollbar())
+            setHasHorizontalScrollbar(hasHorizontalOverflow);
+        if (box().hasAutoVerticalScrollbar())
+            setHasVerticalScrollbar(hasVerticalOverflow);
+    }
+}
+
+void DeprecatedPaintLayerScrollableArea::finalizeScrollDimensions(const DoubleSize& originalScrollOffset, bool autoHorizontalScrollBarChanged, bool autoVerticalScrollBarChanged)
+{
+    ASSERT(box().hasOverflowClip());
 
     // Layout may cause us to be at an invalid scroll position. In this case we need
     // to pull our scroll offsets back to the max (or push them up to the min).
@@ -673,22 +696,8 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
         if (box().style()->overflowY() == OSCROLL && verticalScrollbar())
             verticalScrollbar()->setEnabled(hasVerticalOverflow);
     }
-    if (hasOverlayScrollbars()) {
-        if (!scrollSize(HorizontalScrollbar))
-            setHasHorizontalScrollbar(false);
-        if (!scrollSize(VerticalScrollbar))
-            setHasVerticalScrollbar(false);
-    }
-    // overflow:auto may need to lay out again if scrollbars got added/removed.
-    bool autoHorizontalScrollBarChanged = box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
-    bool autoVerticalScrollBarChanged = box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
 
     if (!visualViewportSuppliesScrollbars() && (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged)) {
-        if (box().hasAutoHorizontalScrollbar())
-            setHasHorizontalScrollbar(hasHorizontalOverflow);
-        if (box().hasAutoVerticalScrollbar())
-            setHasVerticalScrollbar(hasVerticalOverflow);
-
         if (hasVerticalOverflow || hasHorizontalOverflow)
             updateScrollCornerStyle();
 
@@ -738,6 +747,15 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
     positionOverflowControls();
 }
 
+void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
+{
+    DoubleSize originalScrollOffset;
+    bool autoHorizontalScrollBarChanged;

[leviw_travelin_and_unemployed, 2015/08/20 18:53:06]

Kinda sucks that these are necessary and un-used here, but I get it.

[szager1, 2015/08/20 21:53:29]

But they are used: updateScrollDimensions will populate them, and
finalizeScrollDimensions will consume them.

+    bool autoVerticalScrollBarChanged;
+    updateScrollDimensions(originalScrollOffset, autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
+    finalizeScrollDimensions(originalScrollOffset, autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
+}
+
 ScrollBehavior DeprecatedPaintLayerScrollableArea::scrollBehaviorStyle() const
 {
     return box().style()->scrollBehavior();