In order to compute the inline min-content and max-content contributions
of an anonymous block, we were finding its min-content and max-content
inline size with a SizeConstraint coming from the block size of the box.
However, anonymous blocks do not establish a containing block for their
contents, so this patch uses a SizeConstraint from the block size of the
containing block.
Signed-off-by: Oriol Brufau <obrufau@igalia.com>