dart2js: Add support for static fields to new emitter.

sdk/lib/_internal/compiler/implementation/js_emitter/registry.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.
 
 part of dart2js.js_emitter.program_builder;
 
 /// A Fragment maps [LibraryElement]s to their [Element]s.
 ///
 /// Fundamentally, this class nicely encapsulates a
 /// `Map<LibraryElement, List<Element>>`.
 class Fragment {
   final Map<LibraryElement, List<Element>> _mapping =
       <LibraryElement, List<Element>>{};
 
   // It is very common to access the same library multiple times in a row, so
   // we cache the last access.
   LibraryElement _lastLibrary;
   List<Element> _lastElements;
 
   /// A unique name representing this fragment.
   final String name;
   final OutputUnit outputUnit;
 
   Fragment.main(this.outputUnit) : name = "";
-  Fragment.deferred(this.outputUnit, this.name);
+
+  Fragment.deferred(this.outputUnit, this.name) {
+    assert(name != "");
+  }
 
   void add(LibraryElement library, Element element) {
     if (_lastLibrary != library) {
       _lastLibrary = library;
       _lastElements = _mapping.putIfAbsent(library, () => <Element>[]);
     }
     _lastElements.add(element);
   }
 
   int get length => _mapping.length;
@@ skipping 49 matching lines @@
       targetFragment.add(element.library, element);
     }
   }
 
   Holder registerHolder(String name) {
     return _holdersMap.putIfAbsent(
         name,
         () => new Holder(name, _holdersMap.length));
   }
 }