Cleanup model/ct-commit and use every.

-Get rid of url getter. There's no reason not to just
store the url as a regular property.
-Fix revision finder to not be blink specific.
-Don't split the whole message just to get the first line.
-Add tests. I had added tests in my last commit, but it
got lost somehow.
-Use every for computing revision ranges.

NOTRY=true

Review URL: https://codereview.chromium.org/406163003

git-svn-id: svn://svn.chromium.org/blink/trunk@178622 bbb929c8-8fbe-4397-9dbb-9b2b20218538