- it renames '_postMessage' so that it can be overriden by configurations that don't need it.
- it splits the onDone callback in two: onSummary - a callback with all the results, and onDone - a callback with just the end result. The idea is that onSummary is mostly dedicated to reporting results, while onDone is about notifying that unittest is done. This split is very useful for subclasses that only want to override onSummary or onDone.
Review URL: https://codereview.chromium.org//11829045
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@16899 260f80e4-7a28-3924-810f-c04153c831b5
floitsch@google.com