This CL broke the official builders.
Revert 232499 "Move ManifestHandler to top-level extensions."

> Move ManifestHandler to top-level extensions.
> 
> BUG=298586
> R=benwells@chromium.org
> 
> Review URL: https://codereview.chromium.org/52593012

TBR=yoz@chromium.org

Review URL: https://codereview.chromium.org/55713004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232631 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232631