Docserver: Make the hand-written Cron methods return a Future and run first
rather than last, so that they can be parallelised and have the most effect.
Implement a few of the more trivial Cron methods, including moving most
FeaturesBundle methods to return Futures.

BUG=305280
R=jyasskin@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/63203002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233427 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233427