First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/call_site_simple_type_inferer_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.
 
 import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 void compileAndFind(String code,
                     String className,
                     String memberName,
                     bool disableInlining,
                     check(compiler, element)) {
   Uri uri = new Uri(scheme: 'source');
+  asyncStart();
   var compiler = compilerFor(code, uri);
   compiler.disableInlining = disableInlining;
-  compiler.runCompiler(uri);
-  var cls = findElement(compiler, className);
-  var member = cls.lookupLocalMember(buildSourceString(memberName));
-  return check(compiler, member);
+  compiler.runCompiler(uri).then((_) {
+    var cls = findElement(compiler, className);
+    var member = cls.lookupLocalMember(buildSourceString(memberName));
+    return check(compiler, member);
+  }).whenComplete(() => asyncEnd());
 }
 
 const String TEST_1 = r"""
   class A {
     x(p) => p;
   }
   main() { new A().x("s"); }
 """;
 
 const String TEST_2 = r"""
@@ skipping 244 matching lines @@
                                   compiler.typesTask.boolType,
                                   compiler.typesTask.doubleType]);
 
   runTest(TEST_18, (compiler) => [subclassOfInterceptor(compiler),
                                   subclassOfInterceptor(compiler)]);
 }
 
 void main() {
   test();
 }