Watchlists provides an opportunity for someone interested in a particular
code section to make comments before commit. One can subscribe to watchlists
depending on filepath (regular expressions) and she'll automatically get
cc-ed to changes when the watchlist is triggered.

Additional examples of watchlist_rules in diff repo:
http://codereview.chromium.org/118431
http://codereview.chromium.org/119356
Review URL: http://codereview.chromium.org/118432

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@18209 0039d316-1c4b-4281-b951-d872f2087c98