Add overflow:auto scrollbars to child flex basis.

Source/core/layout/LayoutBox.cpp

Index: Source/core/layout/LayoutBox.cpp
diff --git a/Source/core/layout/LayoutBox.cpp b/Source/core/layout/LayoutBox.cpp
index 57c008958978bdd6ca6f506763eac40512b86973..2a122f6b790c015e80886a9b36a752d39729caae 100644
--- a/Source/core/layout/LayoutBox.cpp
+++ b/Source/core/layout/LayoutBox.cpp
@@ -2397,7 +2397,7 @@ LayoutUnit LayoutBox::computeContentAndScrollbarLogicalHeightUsing(SizeType heig
     if (height.isIntrinsic()) {
         if (intrinsicContentHeight == -1)
             return -1; // Intrinsic height isn't available.
-        return computeIntrinsicLogicalContentHeightUsing(height, intrinsicContentHeight, borderAndPaddingLogicalHeight());
+        return computeIntrinsicLogicalContentHeightUsing(height, intrinsicContentHeight, borderAndPaddingLogicalHeight()) + scrollbarLogicalHeight();
     }
     if (height.isFixed())
         return height.value();