First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/closure_codegen_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.
 // Test that parameters keep their names in the output.
 
 import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST_INVOCATION0 = r"""
@@ skipping 34 matching lines @@
   Expect.isTrue(generated.contains(r".call$0()"));
   generated = compile(TEST_INVOCATION1);
   Expect.isTrue(generated.contains(r".call$1(1)"));
   generated = compile(TEST_INVOCATION2);
   Expect.isTrue(generated.contains(r".call$2(1, 2)"));
 }
 
 // Make sure that the bailout version does not introduce a second version of
 // the closure.
 closureBailout() {
-  String generated = compileAll(TEST_BAILOUT);
-  RegExp regexp = new RegExp(r'call\$0: function');
-  Iterator<Match> matches = regexp.allMatches(generated).iterator;
-  checkNumberOfMatches(matches, 1);
+  compileAll(TEST_BAILOUT).then((generated) {
+    RegExp regexp = new RegExp(r'call\$0: function');
+    Iterator<Match> matches = regexp.allMatches(generated).iterator;
+    checkNumberOfMatches(matches, 1);
+  });
 }
 
 main() {
   closureInvocation();
   closureBailout();
 }