First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/import_test.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.
 
 // Test that the compiler can handle missing files used in imports, exports,
 // part tags or as the main source file.
 
 library dart2js.test.import;
 
 import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
 import 'memory_compiler.dart';
 
 const MEMORY_SOURCE_FILES = const {
   'main.dart': '''
 
 library main;
 
 import 'dart:thisLibraryShouldNotExist';
 import 'package:thisPackageShouldNotExist/thisPackageShouldNotExist.dart';
 export 'foo.dart';
 
 part 'bar.dart';
 
 main() {
   int i = "";
 }
 ''',
 };
 
 testMissingImports() {
   var collector = new DiagnosticCollector();
   var compiler = compilerFor(MEMORY_SOURCE_FILES, diagnosticHandler: collector);
-  compiler.run(Uri.parse('memory:main.dart'));
-  Expect.equals(4, collector.errors.length);
-  Expect.equals(1, collector.warnings.length);
+  asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    Expect.equals(4, collector.errors.length);
+    Expect.equals(1, collector.warnings.length);
+  }));
 }
 
 testMissingMain() {
   var collector = new DiagnosticCollector();
   var compiler = compilerFor({}, diagnosticHandler: collector);
-  compiler.run(Uri.parse('memory:missing.dart'));
-  Expect.equals(1, collector.errors.length);
-  Expect.equals(0, collector.warnings.length);
+  asyncTest(() => compiler.run(Uri.parse('memory:missing.dart')).then((_) {
+    Expect.equals(1, collector.errors.length);
+    Expect.equals(0, collector.warnings.length);
+  }));
 }
 
 void main() {
   testMissingImports();
   testMissingMain();
 }