Fix deferred loading with multiple apps on same page.

tests/html/deferred_multi_app.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.
+
+import "deferred_multi_app_lib.dart" deferred as lib;
+import "dart:async";
+import "dart:html";
+import "package:expect/expect.dart";
+
+main() {
+  Element state = querySelector("#state");
+  if (state.text == "1") {
+    lib.loadLibrary().then((_) {
+      var a = lib.one();
+      Expect.equals("one", a);
+      window.postMessage(a, '*');
+    });
+    state.text = "2";
+  } else {
+    new Timer(new Duration(milliseconds: 100), () {
+      lib.loadLibrary().then((_) {
+        var a = lib.two();
+        Expect.equals("two", a);
+        window.postMessage(a, '*');
+      });
+    });
+  }
+}