DevTools: Speedup sourceURL matching

Do not use RegularExpression for sourceURL matching as creation of
a regular expression takes time.

BUG=289714

Review URL: https://chromiumcodereview.appspot.com/24198005

git-svn-id: svn://svn.chromium.org/blink/trunk@158116 bbb929c8-8fbe-4397-9dbb-9b2b20218538