Docserver: Significant refactor to new_github_file_system to try and address
the not-updating bug.

BUG=318878
R=yoz@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/71663003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235289 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235289