feat(tests): add a test injector

fixes #614

Asynchronous test should inject an AsyncTestCompleter:

Before:

  it("async test", (done) => {
    // ...
    done();
  });

After:

  it("async test", inject([AsyncTestCompleter], (async) => {
    // ...
    async.done();
  }));

Note: inject() is currently a function and the first parameter is the
array of DI tokens to inject as the test function parameters. This
construct is linked to Traceur limitations. The planned syntax is:

  it("async test", @Inject (async: AsyncTestCompleter) => {
    // ...
    async.done();
  });

test-main.dart

@@ -2,6 +2,8 @@ import 'package:guinness/guinness.dart';
 import 'package:unittest/unittest.dart' as unit;
 import 'package:angular2/src/dom/browser_adapter.dart';
 
+import 'package:angular2/src/test_lib/test_lib.dart' show testSetup;
+
 main() {
   BrowserDomAdapter.makeCurrent();
   unit.filterStacks = true;
@@ -12,6 +14,8 @@ main() {
 
   guinness.autoInit = false;
   guinness.initSpecs();
+
+  testSetup();
 }
 
 _printWarnings () {
@@ -24,4 +28,4 @@ _printWarnings () {
   if (info.exclusiveDescribes.isNotEmpty) {
     print("WARN: ddescribe caused some tests to be excluded");
   }
-}
+}