chore(test): migrate Dart tests to package:test

Instead of running with karma and the karma-dart shim, run dart
tests directly using the new package:test runner. This migrates
away from package:unittest.

Fixes a couple tests, mostly associated with depending on absolute
URLs or editing the test providers after an injector had already
been created.

Remove karma-dart and associated files. Change gupfiles to run tests
via `pub run test` instead.

modules/angular2/test/core/reflection/reflector_spec.ts

@@ -263,7 +263,7 @@ export function main() {
       describe("importUri", () => {
         it("should return the importUri for a type", () => {
           expect(reflector.importUri(TestObjWith00Args)
-                     .endsWith('base/dist/dart/angular2/test/core/reflection/reflector_spec.dart'))
+                     .endsWith('test/core/reflection/reflector_spec.dart'))
               .toBe(true);
         });
       });