Fix incorrect assumption about children's flexBasis

Source/core/rendering/RenderFlexibleBox.cpp

Index: Source/core/rendering/RenderFlexibleBox.cpp
diff --git a/Source/core/rendering/RenderFlexibleBox.cpp b/Source/core/rendering/RenderFlexibleBox.cpp
index faff63cc332575ce84bb1b4cb80c6037e17c17d7..25956e075f1ea29a132543a0ae5fc7ce75e3a8ef 100644
--- a/Source/core/rendering/RenderFlexibleBox.cpp
+++ b/Source/core/rendering/RenderFlexibleBox.cpp
@@ -611,12 +611,11 @@ LayoutUnit RenderFlexibleBox::preferredMainAxisContentExtentForChild(RenderBox&
     if (preferredMainAxisExtentDependsOnLayout(flexBasis, hasInfiniteLineLength)) {
         LayoutUnit mainAxisExtent;
         if (hasOrthogonalFlow(child)) {
-            if (child.needsLayout() || relayoutChildren) {
+            if (child.needsLayout() || relayoutChildren || !m_intrinsicSizeAlongMainAxis.contains(&child)) {
                 m_intrinsicSizeAlongMainAxis.remove(&child);
                 child.forceChildLayout();
                 m_intrinsicSizeAlongMainAxis.set(&child, child.logicalHeight());
             }
-            ASSERT(m_intrinsicSizeAlongMainAxis.contains(&child));
             mainAxisExtent = m_intrinsicSizeAlongMainAxis.get(&child);
         } else {
             mainAxisExtent = child.maxPreferredLogicalWidth();