test(dirty_checking): port DirtyCheckingChangeDetector tests from Angular.dart

This also tidies up the testing infrastructure a tiny bit to ensure that tests can actually be run.

This is looking good, and it's now possible to begin implementing change detection algorithms using
the DirtyCheckingChangeDetector.

Closing the initial issue, I'll open a new one regarding porting over the other change detection
tests.

Closes #1