Fix MediaQueryTokenizer bug

The MediaQueryTokenizer had a problem with the check if the next chars are a number or an ident.
This CL fixes that bug and changes the implementation terminology to match the spec,
so that bugs like that would be easier to catch.

BUG=377510

Review URL: https://codereview.chromium.org/299323008

git-svn-id: svn://svn.chromium.org/blink/trunk@174896 bbb929c8-8fbe-4397-9dbb-9b2b20218538