First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/private_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
 import 'mock_compiler.dart';
 
 import '../../../sdk/lib/_internal/compiler/implementation/source_file.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
     hide SourceString;
 
 const String PRIVATE_SOURCE_URI = 'src:private';
 const String PRIVATE_SOURCE = '''
 
 var _privateVariable;
@@ skipping 45 matching lines @@
 
                   import '$PRIVATE_SOURCE_URI';
 
                   void main() {
                     PublicClass publicClass;
                     $text
                   }
                   ''';
   Uri uri = Uri.parse('src:public');
   compiler.registerSource(uri, source);
-  compiler.runCompiler(uri);
-  compareWarningKinds(text, expectedWarnings, compiler.warnings);
+  asyncTest(() => compiler.runCompiler(uri).then((_) {
+    compareWarningKinds(text, expectedWarnings, compiler.warnings);
+  }));
 }
 
 void main() {
   // Read from private variable.
   analyze('var value = _privateVariable;', MessageKind.CANNOT_RESOLVE.warning);
   // Write to private variable.
   analyze('_privateVariable = 0;', MessageKind.CANNOT_RESOLVE.warning);
   // Access private function.
   analyze('var value = _privateFunction;', MessageKind.CANNOT_RESOLVE.warning);
   // Call private function.
@@ skipping 74 matching lines @@
   // Call public getter on public class.
   analyze('var value = publicClass.publicGetter;');
   // Call public setter on public class.
   analyze('publicClass.publicSetter = 0;');
   // Access public method on public class.
   analyze('var value = publicClass.publicMethod;');
   // Call public method on public class.
   analyze('publicClass.publicMethod();');
 }