Add browser tags to all of our tests.

test/runner/tag_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 'package:scheduled_test/descriptor.dart' as d;
 import 'package:scheduled_test/scheduled_stream.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
@@ skipping 237 matching lines @@
           test("foo", () {}, tags: "a");
         }
       """).create();
 
       var test = runTest(["-p", "vm,content-shell", "test.dart"]);
       test.stdout.expect(consumeThrough(lines(
           'Warning: A tag was used that wasn\'t specified in dart_test.yaml.\n'
           '  a was used in the test "foo"')));
       test.stdout.expect(never(startsWith("Warning:")));
       test.shouldExit(0);
-    });
+    }, tags: "content-shell");
   });
 
   group("invalid tags", () {
     test("are disallowed by test()", () {
       d.file("test.dart", """
         import 'package:test/test.dart';
 
         void main() {
           test("foo", () {}, tags: "a b");
         }
@@ skipping 59 matching lines @@
   }
 
   // Consume until the end of the warning block, and assert that it has no
   // further tags than the ones we specified.
   yield consumeWhile(isNot(anyOf([contains(" was used in"), isEmpty])));
   yield isEmpty;
 }());
 
 /// Returns a [StreamMatcher] that matches the lines of [string] in order.
 StreamMatcher lines(String string) => inOrder(string.split("\n"));