First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/analyze_helper.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.
 
 library analyze_helper;
 
 import "package:expect/expect.dart";
+import 'dart:async';
 import 'dart:io';
 import '../../../sdk/lib/_internal/compiler/compiler.dart' as api;
 import '../../../sdk/lib/_internal/compiler/implementation/apiimpl.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
     hide Compiler;
 import '../../../sdk/lib/_internal/compiler/implementation/filenames.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/source_file_provider.dart';
 
 /**
  * Map of whitelisted warnings and errors.
@@ skipping 97 matching lines @@
       if (checkWhiteList(uri, message)) {
         // Suppress whitelisted errors.
         return;
       }
       hasErrors = true;
     }
     super.diagnosticHandler(uri, begin, end, message, kind);
   }
 }
 
-void analyze(List<Uri> uriList, Map<String, List<String>> whiteList) {
+Future analyze(List<Uri> uriList, Map<String, List<String>> whiteList) {
   var libraryRoot = currentDirectory.resolve('sdk/');
   var provider = new SourceFileProvider();
   var handler = new CollectingDiagnosticHandler(whiteList, provider);
   var compiler = new Compiler(
       provider.readStringFromUri,
       null,
       handler.diagnosticHandler,
       libraryRoot, libraryRoot,
       <String>['--analyze-only', '--analyze-all',
                '--categories=Client,Server']);
   compiler.librariesToAnalyzeWhenRun = uriList;
-  compiler.run(null);
-  handler.checkResults();
+  return compiler.run(null).then((_) {
+    handler.checkResults();
+  });
 }