Add a --pause-after-load flag for debugging.

pubspec.yaml

 name: test
 
 # This version should really be 0.12.4-dev, but scheduled_test depends on
 # test <0.12.4, so we're using + instead.
 version: 0.12.3+dev
 author: Dart Team <misc@dartlang.org>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test
 environment:
   sdk: '>=1.9.0 <2.0.0'
 dependencies:
   analyzer: '>=0.23.0 <=0.26.0-alpha.0'
   args: '>=0.12.1 <0.14.0'
-  async: '^1.2.0'
+
+  # TODO(nweiz): Bring in a hosted version of async when 1.3.0 is released.
+  async: {git: git://github.com/dart-lang/async.git}
   barback: '>=0.14.0 <0.16.0'
   collection: '^1.1.0'
   crypto: '^0.9.0'
   glob: '^1.0.0'
   http_multi_server: '^1.0.0'
   http_parser: '^0.0.2'
   path: '^1.2.0'
   pool: '^1.1.0'
   pub_semver: '^1.0.0'
   shelf: '>=0.5.3 <0.7.0'
   shelf_static: '^0.2.0'
   shelf_web_socket: '^0.0.1'
   source_map_stack_trace: '^1.0.0'
   source_maps: '^0.10.1'
   source_span: '^1.0.0'
   stack_trace: '^1.2.1'
   string_scanner: '^0.1.1'
   yaml: '>=0.9.0 <3.0.0'
 
   # Use a tight version constraint to ensure that a constraint on matcher
   # properly constrains all features it provides.
   matcher: '>=0.12.0 <0.12.1'
 dev_dependencies:
   fake_async: '^0.1.2'
   scheduled_test: '^0.12.2'