First pass at asynchronous input loading in dart2js.

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

Index: sdk/lib/_internal/compiler/implementation/deferred_load.dart
diff --git a/sdk/lib/_internal/compiler/implementation/deferred_load.dart b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
index 1a8d77008f73be06af0e7b38b1200fe153ad33ff..f2b257cfd7f9c8331cdb4fcc1dd6f7a2fd8ae48e 100644
--- a/sdk/lib/_internal/compiler/implementation/deferred_load.dart
+++ b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
@@ -4,6 +4,7 @@
 
 library deferred_load;
 
+import 'dart:async';
 import 'dart:collection'
        show LinkedHashMap,
             LinkedHashSet;
@@ -63,8 +64,9 @@ class DeferredLoadTask extends CompilerTask {
 
   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(