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 39 matching lines @@
   /// DeferredLibrary from dart:async
   ClassElement get deferredLibraryClass {
     if (cachedDeferredLibraryClass == null) {
       cachedDeferredLibraryClass = findDeferredLibraryClass();
     }
     return cachedDeferredLibraryClass;
   }
 
   ClassElement findDeferredLibraryClass() {
     var uri = new Uri(scheme: 'dart', path: 'async');
+    // TODO(rnystrom): Handle future.

[Bob Nystrom, 2013/06/26 01:03:24]

I still have to get this working. This is a bit harder because we don't get here
until much later in the compile process and I'd like all async stuff to be done
by now.

One option would be to just load "dart:async" at the same time we load other
libraries early on and then pass it to this task. Thoughts?

[ahe, 2013/06/26 07:02:00]

Actually, I think this is easy to fix.  I just need to slightly rewrite this
code, which should also make the compiler faster by not scanning dart:async
unless it really is needed. I'll handle this.

[Bob Nystrom, 2013/06/27 00:38:18]

This is breaking a couple of tests. Should I file a bug and mark them failing,
or should I try to get them passing?

     LibraryElement asyncLibrary =
-        compiler.libraryLoader.loadLibrary(uri, null, uri);
+        deprecatedFutureValue(compiler.libraryLoader.loadLibrary(uri, null, uri));
     var element = asyncLibrary.find(const SourceString('DeferredLibrary'));
     if (element == null) {
       compiler.internalErrorOnElement(
           asyncLibrary,
           'dart:async library does not contain required class: '
           'DeferredLibrary');
     }
     return element;
   }
 
@@ skipping 178 matching lines @@
     TreeElements elements =
         compiler.enqueuer.resolution.getCachedElements(element);
     if (elements == null) return new LinkedHashSet<Element>();
     Node node = element.parseNode(compiler);
     var collector = new DependencyCollector(elements, compiler);
     node.accept(collector);
     collector.dependencies.addAll(elements.otherDependencies);
     return collector.dependencies;
   }
 }