Add better support for async tests in run.js

pkg/dev_compiler/tool/run.js

 // Copyright (c) 2016, 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 is a utility to run and debug an individual DDC compiled test.
 /// Tests can be run with either node or devtool (a Chrome-based utility with
 /// DOM APIs and developer tools support).
 ///
 /// Install devtool via:
 /// > npm install -g devtool
@@ skipping 25 matching lines @@
     path: ddcdir + 'gen/codegen_output/pkg/path',
     stack_trace: ddcdir + 'gen/codegen_output/pkg/stack_trace',
     unittest: ddcdir + 'gen/codegen_output/pkg/unittest',
   }
 });
 
 // TODO(vsm): Factor out test framework code in test/browser/language_tests.js
 // and use here.  Async tests and unittests won't work without it.
 var sdk = requirejs('dart_sdk');
 sdk.dart.ignoreWhitelistedErrors(false);
+
+function finish(e) {
+  if (e) {
+    console.log('Test ' + test + ' failed:\n' + e.toString());
+    sdk.dart.stackPrint(e);
+  } else {
+    console.log('Test ' + test + ' passed.');
+  }
+}
+
+var async_helper = requirejs('async_helper').async_helper;
+async_helper.asyncTestInitialize(finish);
+
 var module = requirejs(test);
 var lib = test.split('/').slice(-1)[0];
 try {
-  sdk._isolate_helper.startRootIsolate(module[lib].main, []);
-  console.log('Test ' + test + ' passed.');
+  var result = sdk._isolate_helper.startRootIsolate(module[lib].main, []);
+  // async_helper tests call finish directly - call here for all other
+  // tests.
+  if (!async_helper.asyncTestStarted) {
+    if (!result || !(result instanceof dart_sdk.async.Future)) {
+      finish();
+    } else {
+      // Wait iff result is a future
+      result.then(dart_sdk.dart.dynamic)(() => finish());
+    }
+  }
 } catch (e) {
-  console.log('Test ' + test + ' failed:\n' + e.toString());
-  sdk.dart.stackPrint(e);
+  finish(e);
 }