Docserver: 2 changes to address issues with site.css 404-ing on the docserver.
Firstly, during cron runs read from the newest svn revision, not HEAD, so that
data doesn't change underneath unexpectedly. I believe this is the main cause of
failure. Secondly, don't attempt to share the caches across app versions. The
site.css failure tends to happen on *every* recent version of the app at once,
and this is likely to be why.

I am pretty sure that these failures are not site.css specific, it's just that
when that file fails it's very noticeable.

BUG=301733
R=jyasskin@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/25428005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226917 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226917