Revert 232631 - Revert 232499 "Move ManifestHandler to top-level extensions."

Was not the cause of breakage. See bug for that.

BUG=314916
R=benwells@chromium.org
TBR=benwells@chromium.org

Review URL: https://codereview.chromium.org/60393005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233308 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233308