text-overflow on flexbox should have no effect

Since flexbox doesn't have any direct inline children, text-overflow
should have no effect. There is code that checks for the parent's
text-overflow style, but that should be limited to blocks where we
created anon blocks because of mixed inlines and blocks -- grid and flex
should not be affected.

See also this thread:
http://lists.w3.org/Archives/Public/www-style/2013Sep/0070.html

R=ojan@chromium.org,jchaffraix@chromium.org
BUG=285943

Review URL: https://chromiumcodereview.appspot.com/23449034

git-svn-id: svn://svn.chromium.org/blink/trunk@157795 bbb929c8-8fbe-4397-9dbb-9b2b20218538