Revert "only run the admin server if admin-port is specified"

This reverts commit 9ed84a9d820a57132d915cd069b47b33ed6f5631.

BUG=
R=scheglov@google.com

Review URL: https://codereview.chromium.org//565813004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@40299 260f80e4-7a28-3924-810f-c04153c831b5