Add overflow:auto scrollbars to child flex basis.

Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 624 matching lines @@
 void DeprecatedPaintLayerScrollableArea::scrollToOffset(const DoubleSize& scrollOffset, ScrollOffsetClamping clamp, ScrollBehavior scrollBehavior)
 {
     cancelProgrammaticScrollAnimation();
     DoubleSize newScrollOffset = clamp == ScrollOffsetClamped ? clampScrollOffset(scrollOffset) : scrollOffset;
     if (newScrollOffset != adjustedScrollOffset()) {
         DoublePoint origin(scrollOrigin());
         ScrollableArea::setScrollPosition(-origin + newScrollOffset, ProgrammaticScroll, scrollBehavior);
     }
 }
 
-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).
     DoubleSize clampedScrollOffset = clampScrollOffset(adjustedScrollOffset());
     if (clampedScrollOffset != adjustedScrollOffset())
         scrollToOffset(clampedScrollOffset);
 
     if (originalScrollOffset != adjustedScrollOffset()) {
         DoublePoint origin(scrollOrigin());
         scrollPositionChanged(-origin + adjustedScrollOffset(), ProgrammaticScroll);
     }
 
     bool hasHorizontalOverflow = this->hasHorizontalOverflow();
     bool hasVerticalOverflow = this->hasVerticalOverflow();
 
     {
         // Hits in compositing/overflow/automatically-opt-into-composited-scrolling-after-style-change.html.
         DisableCompositingQueryAsserts disabler;
 
         // overflow:scroll should just enable/disable.
         if (box().style()->overflowX() == OSCROLL && horizontalScrollbar())
             horizontalScrollbar()->setEnabled(hasHorizontalOverflow);
         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();
 
         layer()->updateSelfPaintingLayer();
 
         // Force an update since we know the scrollbars have changed things.
         if (box().document().hasAnnotatedRegions())
             box().document().setAnnotatedRegionsDirty(true);
 
         if (box().style()->overflowX() == OAUTO || box().style()->overflowY() == OAUTO) {
@@ skipping 29 matching lines @@
         }
     }
 
     bool hasOverflow = hasScrollableHorizontalOverflow() || hasScrollableVerticalOverflow();
     updateScrollableAreaSet(hasOverflow);
 
     DisableCompositingQueryAsserts disabler;
     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();
 }
 
 bool DeprecatedPaintLayerScrollableArea::hasHorizontalOverflow() const
 {
     return pixelSnappedScrollWidth() > box().pixelSnappedClientWidth();
 }
 
@@ skipping 700 matching lines @@
         return false;
 
     LocalFrame* frame = box().frame();
     if (!frame || !frame->isMainFrame() || !frame->settings())
         return false;
 
     return frame->settings()->viewportMetaEnabled();
 }
 
 } // namespace blink