[css-flexbox] Don't force layout for overflow: auto anymore

third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 877 matching lines @@
     bool definite = child.computePercentageLogicalHeight(length) != -1;
     m_hasDefiniteHeight =
         definite ? SizeDefiniteness::Definite : SizeDefiniteness::Indefinite;
     return definite;
   }
   // TODO(cbiesinger): Eventually we should support other types of sizes here.
   // Requires updating computeMainSizeFromAspectRatioUsing.
   return length.isFixed();
 }
 
-bool LayoutFlexibleBox::childFlexBaseSizeRequiresLayout(
-    const LayoutBox& child) const {
-  return (!mainAxisLengthIsDefinite(child, flexBasisForChild(child)) &&
-          (hasOrthogonalFlow(child) ||
-           (crossAxisOverflowForChild(child) == OverflowAuto &&
-            !PaintLayerScrollableArea::FreezeScrollbarsScope::
-                scrollbarsAreFrozen())));
-}
-
 void LayoutFlexibleBox::cacheChildMainSize(const LayoutBox& child) {
   DCHECK(!child.needsLayout());
   LayoutUnit mainSize;
   if (hasOrthogonalFlow(child)) {
     mainSize = child.logicalHeight();
   } else {
     // The max preferred logical width includes the intrinsic scrollbar logical
     // width, which is only set for overflow: scroll. To handle overflow: auto,
     // we have to take scrollbarLogicalWidth() into account, and then subtract
     // the intrinsic width again so as to not double-count overflow: scroll
@@ skipping 20 matching lines @@
     UseCounter::count(document(), UseCounter::AspectRatioFlexItem);
 
   Length flexBasis = flexBasisForChild(child);
   if (mainAxisLengthIsDefinite(child, flexBasis))
     return std::max(LayoutUnit(), computeMainAxisExtentForChild(
                                       child, MainOrPreferredSize, flexBasis));
 
   if (child.styleRef().containsSize())
     return LayoutUnit();
 
+  // The flex basis is indefinite (=auto), so we need to compute the actual
+  // width of the child. For the logical width axis we just use the preferred
+  // width; for the height we need to lay out the child.
   LayoutUnit mainAxisExtent;
-  if (childFlexBaseSizeRequiresLayout(child)) {
+  if (hasOrthogonalFlow(child)) {
     if (childLayoutType == NeverLayout)
       return LayoutUnit();
 
     updateBlockChildDirtyBitsBeforeLayout(childLayoutType == ForceLayout,
                                           child);
     if (child.needsLayout() || childLayoutType == ForceLayout ||
         !m_intrinsicSizeAlongMainAxis.contains(&child)) {
       child.forceChildLayout();
       cacheChildMainSize(child);
     }
     mainAxisExtent = m_intrinsicSizeAlongMainAxis.get(&child);
   } else {
-    // We don't need to add scrollbarLogicalWidth here. For overflow: scroll,
-    // the preferred width already includes the scrollbar size (via
-    // scrollbarLogicalWidth()). For overflow: auto,
-    // childFlexBaseSizeRequiresLayout returns true and we handle that via the
-    // other branch of this if.
+    // We don't need to add scrollbarLogicalWidth here because the preferred
+    // width includes the scrollbar, even for overflow: auto.
     mainAxisExtent = child.maxPreferredLogicalWidth();
   }
   DCHECK_GE(mainAxisExtent - mainAxisBorderAndPadding, LayoutUnit())
       << mainAxisExtent << " - " << mainAxisBorderAndPadding;
   return mainAxisExtent - mainAxisBorderAndPadding;
 }
 
 void LayoutFlexibleBox::layoutFlexItems(bool relayoutChildren,
                                         SubtreeLayoutScope& layoutScope) {
   Vector<LineContext> lineContexts;
@@ skipping 1322 matching lines @@
       LayoutUnit originalOffset =
           lineContexts[lineNumber].crossAxisOffset - crossAxisStartEdge;
       LayoutUnit newOffset =
           contentExtent - originalOffset - lineCrossAxisExtent;
       adjustAlignmentForChild(*child, newOffset - originalOffset);
     }
   }
 }
 
 }  // namespace blink