First pass at asynchronous input loading in dart2js.

sdk/lib/_internal/compiler/implementation/deferred_load.dart

 // Copyright (c) 2013, 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.
 
 library deferred_load;
 
+import 'dart:async';
 import 'dart:collection'
        show LinkedHashMap,
             LinkedHashSet;
 
 import 'dart2jslib.dart'
        show Compiler,
             CompilerTask,
             ConstructedConstant,
             MessageKind,
             SourceString,
@@ skipping 23 matching lines @@
   final Set<LibraryElement> deferredLibraries =
       new LinkedHashSet<LibraryElement>();
 
   /// Records all elements that are deferred.
   ///
   /// Long term, we want to split deferred element into more than one
   /// file (one for each library that is deferred), and this field
   /// should become obsolete.
   final Set<Element> allDeferredElements = new LinkedHashSet<Element>();
 
-  ClassElement cachedDeferredLibraryClass;
-
   DeferredLoadTask(Compiler compiler) : super(compiler);
 
   String get name => 'Deferred Loading';
 
   /// DeferredLibrary from dart:async
   ClassElement get deferredLibraryClass => compiler.deferredLibraryClass;
 
   bool get areAnyElementsDeferred => !allDeferredElements.isEmpty;
 
   bool isDeferred(Element element) {
@@ skipping 180 matching lines @@
         compiler.enqueuer.resolution.getCachedElements(element);
     if (elements == null) return new LinkedHashSet<Element>();
     Node node = element.parseNode(compiler);
     if (node == null) return new LinkedHashSet<Element>();
     var collector = new DependencyCollector(elements, compiler);
     node.accept(collector);
     collector.dependencies.addAll(elements.otherDependencies);
     return collector.dependencies;
   }
 }