after an isolate is created and initialized.
Added an option --use_script_snapshot which creates a snapshot of the specified script in an isolate, shuts that down and restarts on a new isolate and loads the script from the snapshot buffer and executes it.
Review URL: http://codereview.chromium.org//8970004
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@2609 260f80e4-7a28-3924-810f-c04153c831b5