watchlist: Add the filename pattern for definitions.

watchlist: Add the filename pattern for definitions.
https://bugs.webkit.org/show_bug.cgi?id=68917

Reviewed by Adam Barth.

* Scripts/webkitpy/common/watchlist/filenamepattern.py: Added.
* Scripts/webkitpy/common/watchlist/filenamepattern_unittest.py: Added.
* Scripts/webkitpy/common/watchlist/watchlist.py: Added the filename pattern
for definitions.
* Scripts/webkitpy/common/watchlist/watchlist_unittest.py: Added tests.
* Scripts/webkitpy/common/watchlist/watchlistparser_unittest.py: Typo fix.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96144 268f45cc-cd09-0410-ab3c-d52691b4dbfc