First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/unneeded_part_js_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 no parts are emitted when deferred loading isn't used.
 
 import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
 import 'memory_source_file_helper.dart';
 
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
        show NullSink;
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart'
        show Diagnostic;
 
 import 'dart:async';
 
 main() {
   Uri script = currentDirectory.resolve(nativeToUriPath(Platform.script));
   Uri libraryRoot = script.resolve('../../../sdk/');
   Uri packageRoot = script.resolve('./packages/');
 
-  MemorySourceFileProvider.MEMORY_SOURCE_FILES = MEMORY_SOURCE_FILES;
-  var provider = new MemorySourceFileProvider();
+  var provider = new MemorySourceFileProvider(MEMORY_SOURCE_FILES);
   void diagnosticHandler(Uri uri, int begin, int end,
                          String message, Diagnostic kind) {
     if (kind == Diagnostic.VERBOSE_INFO) {
       return;
     }
     throw '$uri:$begin:$end:$message:$kind';
   }
 
   EventSink<String> outputProvider(String name, String extension) {
     if (name != '') throw 'Attempt to output file "$name.$extension"';
     return new NullSink('$name.$extension');
   }
 
   Compiler compiler = new Compiler(provider.readStringFromUri,
                                    outputProvider,
                                    diagnosticHandler,
                                    libraryRoot,
                                    packageRoot,
                                    []);
-  compiler.run(Uri.parse('memory:main.dart'));
-  Expect.isFalse(compiler.compilationFailed);
+  asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    Expect.isFalse(compiler.compilationFailed);
+  }));
 }
 
 const Map MEMORY_SOURCE_FILES = const {
   'main.dart': """
 class Greeting {
   final message;
   const Greeting(this.message);
 }
 
 const fisk = const Greeting('Hello, World!');
 
 main() {
   var x = fisk;
   if (new DateTime.now().millisecondsSinceEpoch == 42) {
     x = new Greeting(\"I\'m confused\");
   }
   print(x.message);
 }
 """,
 };