Respect top-level @TestOn declarations.

test/runner/parse_metadata_test.dart

 // Copyright (c) 2015, 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.
 
+@TestOn("vm")
+
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:unittest/unittest.dart';
+import 'package:unittest/src/backend/platform_selector.dart';
+import 'package:unittest/src/backend/test_platform.dart';
 import 'package:unittest/src/runner/parse_metadata.dart';
 
 String _sandbox;
 String _path;
 
 void main() {
   setUp(() {
     _sandbox = Directory.systemTemp.createTempSync('unittest_').path;
     _path = p.join(_sandbox, "test.dart");
   });
 
   tearDown(() {
     new Directory(_sandbox).deleteSync(recursive: true);
   });
 
   test("returns empty metadata for an empty file", () {
     new File(_path).writeAsStringSync("");
     var metadata = parseMetadata(_path);
-    expect(metadata.testOn, isNull);
+    expect(metadata.testOn, equals(PlatformSelector.all));
   });
 
   test("ignores irrelevant annotations", () {
     new File(_path).writeAsStringSync("@Fblthp\n@Fblthp.foo\nlibrary foo;");
     var metadata = parseMetadata(_path);
-    expect(metadata.testOn, isNull);
+    expect(metadata.testOn, equals(PlatformSelector.all));
   });
 
   test("parses a valid annotation", () {
-    new File(_path).writeAsStringSync("@TestOn('foo')\nlibrary foo;");
+    new File(_path).writeAsStringSync("@TestOn('vm')\nlibrary foo;");
     var metadata = parseMetadata(_path);
-    expect(metadata.testOn, equals("foo"));
+    expect(metadata.testOn.evaluate(TestPlatform.vm), isTrue);
+    expect(metadata.testOn.evaluate(TestPlatform.chrome), isFalse);
   });
 
   test("parses a prefixed annotation", () {
     new File(_path).writeAsStringSync(
-        "@foo.TestOn('foo')\n"
+        "@foo.TestOn('vm')\n"
         "import 'package:unittest/unittest.dart' as foo;");
     var metadata = parseMetadata(_path);
-    expect(metadata.testOn, equals("foo"));
+    expect(metadata.testOn.evaluate(TestPlatform.vm), isTrue);
+    expect(metadata.testOn.evaluate(TestPlatform.chrome), isFalse);
   });
 
   test("ignores a constructor named TestOn", () {
     new File(_path).writeAsStringSync("@foo.TestOn('foo')\nlibrary foo;");
     var metadata = parseMetadata(_path);
-    expect(metadata.testOn, isNull);
+    expect(metadata.testOn, equals(PlatformSelector.all));
   });
 
   group("throws an error for", () {
     test("a named constructor", () {
       new File(_path).writeAsStringSync("@TestOn.name('foo')\nlibrary foo;");
       expect(() => parseMetadata(_path), throwsFormatException);
     });
 
     test("no argument list", () {
       new File(_path).writeAsStringSync("@TestOn\nlibrary foo;");
@@ skipping 21 matching lines @@
       expect(() => parseMetadata(_path), throwsFormatException);
     });
 
     test("multiple @TestOns", () {
       new File(_path).writeAsStringSync(
           "@TestOn('foo')\n@TestOn('bar')\nlibrary foo;");
       expect(() => parseMetadata(_path), throwsFormatException);
     });
   });
 }