Set up trial experiment so that password generation is enabled for 10% of the dev/beta users.

BUG=240559,295787

Review URL: https://codereview.chromium.org/23934011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226860 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226860