[css-flexbox] Performance optimization: Only apply min-width: auto when flex-shrinking an item

Source/core/layout/LayoutFlexibleBox.cpp

Index: Source/core/layout/LayoutFlexibleBox.cpp
diff --git a/Source/core/layout/LayoutFlexibleBox.cpp b/Source/core/layout/LayoutFlexibleBox.cpp
index c7212bed4904545c273a0aafc5ccc0924b489b38..11500b2cf3d367ed75b1e92a76c377fe4a62f32b 100644
--- a/Source/core/layout/LayoutFlexibleBox.cpp
+++ b/Source/core/layout/LayoutFlexibleBox.cpp
@@ -834,7 +834,7 @@ void LayoutFlexibleBox::prepareOrderIteratorAndMargins()
     }
 }
 
-LayoutUnit LayoutFlexibleBox::adjustChildSizeForMinAndMax(LayoutBox& child, LayoutUnit childSize)
+LayoutUnit LayoutFlexibleBox::adjustChildSizeForMinAndMax(LayoutBox& child, LayoutUnit childSize, bool childShrunk)
 {
     Length max = isHorizontalFlow() ? child.style()->maxWidth() : child.style()->maxHeight();
     LayoutUnit maxExtent = -1;
@@ -851,7 +851,7 @@ LayoutUnit LayoutFlexibleBox::adjustChildSizeForMinAndMax(LayoutBox& child, Layo
         // computeMainAxisExtentForChild can return -1 when the child has a percentage
         // min size, but we have an indefinite size in that axis.
         minExtent = std::max(LayoutUnit(), minExtent);
-    } else if (min.isAuto() && mainAxisOverflowForChild(child) == OVISIBLE) {
+    } else if (childShrunk && min.isAuto() && mainAxisOverflowForChild(child) == OVISIBLE) {
         // css-flexbox section 4.5
         LayoutUnit contentSize = computeMainAxisExtentForChild(child, MinSize, Length(MinContent));
         ASSERT(contentSize >= 0);
@@ -905,7 +905,7 @@ bool LayoutFlexibleBox::computeNextFlexLine(OrderedFlexItemList& orderedChildren
             + (isHorizontalFlow() ? child->marginWidth() : child->marginHeight());
         LayoutUnit childFlexBaseSize = childMainAxisExtent + childMainAxisMarginBorderPadding;
 
-        LayoutUnit childMinMaxAppliedMainAxisExtent = adjustChildSizeForMinAndMax(*child, childMainAxisExtent);
+        LayoutUnit childMinMaxAppliedMainAxisExtent = adjustChildSizeForMinAndMax(*child, childMainAxisExtent, false);

[leviw_travelin_and_unemployed, 2015/04/17 19:17:40]

Maybe make the parameter default to false to avoid this nasty "false".

[cbiesinger, 2015/04/17 19:39:25]

Done.

         LayoutUnit childHypotheticalMainSize = childMinMaxAppliedMainAxisExtent + childMainAxisMarginBorderPadding;
 
         if (isMultiline() && sumHypotheticalMainSize + childHypotheticalMainSize > lineBreakLength && lineHasInFlowItem)
@@ -954,14 +954,17 @@ bool LayoutFlexibleBox::resolveFlexibleLengths(FlexSign flexSign, const OrderedF
             LayoutUnit preferredChildSize = preferredMainAxisContentExtentForChild(*child);
             LayoutUnit childSize = preferredChildSize;
             double extraSpace = 0;
-            if (availableFreeSpace > 0 && totalFlexGrow > 0 && flexSign == PositiveFlexibility && std::isfinite(totalFlexGrow))
+            bool childShrunk = false;
+            if (availableFreeSpace > 0 && totalFlexGrow > 0 && flexSign == PositiveFlexibility && std::isfinite(totalFlexGrow)) {
                 extraSpace = availableFreeSpace * child->style()->flexGrow() / totalFlexGrow;
-            else if (availableFreeSpace < 0 && totalWeightedFlexShrink > 0 && flexSign == NegativeFlexibility && std::isfinite(totalWeightedFlexShrink))
+            } else if (availableFreeSpace < 0 && totalWeightedFlexShrink > 0 && flexSign == NegativeFlexibility && std::isfinite(totalWeightedFlexShrink) && child->style()->flexShrink()) {
                 extraSpace = availableFreeSpace * child->style()->flexShrink() * preferredChildSize / totalWeightedFlexShrink;
+                childShrunk = true;
+            }
             if (std::isfinite(extraSpace))
                 childSize += LayoutUnit::fromFloatRound(extraSpace);
 
-            LayoutUnit adjustedChildSize = adjustChildSizeForMinAndMax(*child, childSize);
+            LayoutUnit adjustedChildSize = adjustChildSizeForMinAndMax(*child, childSize, childShrunk);
             ASSERT(adjustedChildSize >= 0);
             childSizes.append(adjustedChildSize);
             usedFreeSpace += adjustedChildSize - preferredChildSize;