Always initialize top-level `Isolate` for deferred libraries.

tests/language/deferred_only_constant_test.dart

 // Copyright (c) 2014, 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.
 
-// Test generation of 'dynamic' type literals.
+// Testing import of only constants from a deferred library.
 
-import "package:expect/expect.dart";
+import "deferred_only_constant_lib.dart" deferred as lib;
 
 void main() {
-  Expect.isTrue(dynamic is Type);
-  Expect.isFalse(dynamic == Type);
-}
+  lib.loadLibrary().then((_) {
+    print(lib.constant);

[floitsch, 2014/09/29 10:35:59]

Expect.equals(...) ?

[sigurdm, 2014/09/29 10:39:29]

Done.

+  });
+}