Call asyncEnd only on success.

tests/compiler/dart2js/analyze_all_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 import "compiler_helper.dart";
 import "package:async_helper/async_helper.dart";
 
 const String SOURCE = """
 class Foo {
@@ skipping 11 matching lines @@
 
 @Foo('y')
 class MyClass {}
 
 main() {
 }
 """;
 
 main() {
   Uri uri = Uri.parse('test:code');
-  asyncStart();
   var compiler1 = compilerFor(SOURCE, uri, analyzeAll: false);
-  compiler1.runCompiler(uri).then((_) {
+  asyncTest(() => compiler1.runCompiler(uri).then((_) {
     Expect.isFalse(compiler1.compilationFailed);
     print(compiler1.warnings);
     Expect.isTrue(compiler1.warnings.isEmpty, 'unexpected warnings');
     Expect.isTrue(compiler1.errors.isEmpty, 'unexpected errors');
-  }).whenComplete(() => asyncEnd());
+  }));
 
-  asyncStart();
   var compiler2 = compilerFor(SOURCE, uri, analyzeAll: true);
-  compiler2.runCompiler(uri).then((_) {
+  asyncTest(() => compiler2.runCompiler(uri).then((_) {
     Expect.isTrue(compiler2.compilationFailed);
     Expect.isTrue(compiler2.warnings.isEmpty, 'unexpected warnings');
     Expect.equals(2, compiler2.errors.length,
                   'expected exactly two errors, but got ${compiler2.errors}');
 
     Expect.equals(MessageKind.CONSTRUCTOR_IS_NOT_CONST,
                   compiler2.errors[0].message.kind);
     Expect.equals("Foo", compiler2.errors[0].node.toString());
 
     Expect.equals(MessageKind.CONSTRUCTOR_IS_NOT_CONST,
                   compiler2.errors[1].message.kind);
     Expect.equals("Foo", compiler2.errors[1].node.toString());
-  }).whenComplete(() => asyncEnd());
+  }));
 }