First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/bad_loop_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 'memory_source_file_helper.dart';
+import "package:async_helper/async_helper.dart";
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart'
        show Diagnostic;
 
 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);
   int warningCount = 0;
   int errorCount = 0;
   void diagnosticHandler(Uri uri, int begin, int end,
                          String message, Diagnostic kind) {
     if (kind == Diagnostic.VERBOSE_INFO) {
       return;
     }
     if (kind == Diagnostic.ERROR) {
       errorCount++;
     } else if (kind == Diagnostic.WARNING) {
       warningCount++;
     } else {
       throw 'unexpected diagnostic $kind: $message';
     }
   }
 
   Compiler compiler = new Compiler(provider.readStringFromUri,
                                    (name, extension) => null,
                                    diagnosticHandler,
                                    libraryRoot,
                                    packageRoot,
                                    ['--analyze-only']);
-  compiler.run(Uri.parse('memory:main.dart'));
-  Expect.isTrue(compiler.compilationFailed);
-  Expect.equals(5, errorCount);
-  Expect.equals(1, warningCount);
+  asyncStart();
+  compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    Expect.isTrue(compiler.compilationFailed);
+    Expect.equals(5, errorCount);
+    Expect.equals(1, warningCount);
+  }).whenComplete(() => asyncEnd());
 }
 
 const Map MEMORY_SOURCE_FILES = const {
   'main.dart': """
 main() {
   for (var x, y in []) {
   }
 
   for (var x = 10 in []) {
   }
 
   for (x.y in []) { // Also causes a warning "x unresolved".
   }
 
   for ((){}() in []) {
   }
 
   for (1 in []) {
   }
 }
 """
 };