Flex box word-wrap is not adhering to spec

The items that are set to flex-wrap and have a single flex line currently
has their cross size adjusted according to the max of the items cross size.
According to the specification section 9.4 number 8 point, it states that:

If the flex container has only one flex line (_even if it’s a multi-line
flex container_) and has a definite cross size the cross size of the flex line
is the flex container’s inner cross size.

link: http://www.w3.org/TR/2014/WD-css-flexbox-1-20140325/#cross-sizing

This patch fixes this bug by removing the condtion that checks if it's
a multiline container or not and based on that set flex line cross size.

Bug=362848

Review URL: https://codereview.chromium.org/324073003

git-svn-id: svn://svn.chromium.org/blink/trunk@176000 bbb929c8-8fbe-4397-9dbb-9b2b20218538