Generate a discovery doc without starting the server.
Generate a discovery doc without starting the server.

R=devoncarew@google.com, lukechurch@google.com
BUG=

Review URL: https://codereview.chromium.org/948873002

kasperpeulen/dart-services,kasperpeulen/dart-services,kasperpeulen/dart-services,dart-lang/dart-services,dart-lang/dart-services,dart-lang/dart-services