Bring back initPolymer, allow boot.js only if using "polymer_experimental.html".

pkg/polymer/lib/src/static_loader.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.
+
+/// Alternative implementation for loading initializers that avoids using
+/// mirrors. Unlike `mirror_loader` this is used for deployed applications to
+/// avoid any dependence on the mirror system.
+library polymer.src.static_loader;
+
+/// Set of initializers that are invoked by `initPolymer`.  This is initialized
+/// with code automatically generated by the polymer transformers. The
+/// initialization code is injected in the entrypoint of the application.
+List<Function> initializers;
+
+/// True if we're in deployment mode.
+// TODO(sigmund): make this a const and remove the assignment in
+// configureForDevelopment when our testing infrastructure supports calling pub
+// build.
+bool deployMode = true;