A (column) flexbox should take min-height into account for sizing

Per http://dev.w3.org/csswg/css-flexbox/#intrinsic-sizes

"The max-content main size of a flex container is the sum of the flex
container's items' max-content contributions. The min-content main size
of a single-line flex container is the sum of the flex container's
items' min-content contributions"

"The main-size min-content/max-content contribution of a flex item is
its outer hypothetical main size when sized under a
min-content/max-content constraint (respectively)."

plus 9.2:
"The hypothetical main size is the item's flex base size clamped
according to its min and max main size properties."

Therefore, when we calculate containerMainInnerSize, we should use
sumHypotheticalMainSize instead of sumFlexBaseSize.

R=ojan@chromium.org
BUG=249551

Review URL: https://chromiumcodereview.appspot.com/18179008

git-svn-id: svn://svn.chromium.org/blink/trunk@153297 bbb929c8-8fbe-4397-9dbb-9b2b20218538