Tests2

@dinhviethoa @keertip 

This is the 2nd half of the continuous testing CL. This:
- adds a command-line tool that can drive Spark tests
- tweaks the spark_test.dart file w/ changes necessary to communicate w/ the test listener
- brings in a dependency on package:chrome_gen. This package has more full-featured support for chrome sockets. It can be used in tandem with package:chrome.