Run dart2js tests unmodified in drt.

dart/pkg/unittest/config.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /** This file is sourced by unitest.dart. */
 
 /**
  * Hooks to configure the unittest library for different platforms. This class
  * implements the API in a platform-independent way. Tests that want to take
  * advantage of the platform can create a subclass and override methods from
@@ skipping 19 matching lines @@
    * even before tests are added to the test framework. It might be used to
    * determine/debug errors that occur before the test harness starts executing.
    */
   void onInit() {}
 
   /**
    * Called as soon as the unittest framework starts running. Used commonly to
    * tell the vm or browser that tests are still running and the process should
    * wait until they are done.
    */
-  void onStart() {}
+  void onStart() {
+    _postMessage('unittest-suite-wait-for-done');
+  }
 
   /**
    * Called when each test starts. Useful to show intermediate progress on
    * a test suite.
    */
   void onTestStart(TestCase testCase) {
     currentTestCase = testCase;
   }
 
   /**
@@ skipping 63 matching lines @@
     } else if (failed == 0 && errors == 0 && uncaughtError == null) {
       print('All $passed tests passed.');
       success = true;
     } else {
       if (uncaughtError != null) {
         print('Top-level uncaught error: $uncaughtError');
       }
       print('$passed PASSED, $failed FAILED, $errors ERRORS');
     }
 
-    // An exception is used by the test infrastructure to detect failure.
-    if (!success) throw new Exception("Some tests failed.");
+    if (success) {
+      _postMessage('unittest-suite-success');
+    } else {
+      throw new Exception('Some tests failed.');
+    }
   }
 
   String _indent(String str) {
     // TODO(nweiz): Use this simpler code once issue 2980 is fixed.
     // return str.replaceAll(const RegExp("^", multiLine: true), "  ");
 
     return Strings.join(str.split("\n").map((line) => "  $line"), "\n");
   }
 
   /** Handle errors that happen outside the tests. */
   // TODO(vsm): figure out how to expose the stack trace here
   // Currently e.message works in dartium, but not in dartc.
   handleExternalError(e, String message) =>
       _reportTestError('$message\nCaught $e', '');
+
+  _postMessage(String message) {
+    // In dart2js browser tests, the JavaScript-based test controller
+    // intercepts calls to print and listens for "secret" messages.
+    print(message);
+  }
 }