First pass at asynchronous input loading in dart2js.

tests/compiler/dart2js/missing_file_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 the compiler can handle imports when package root has not been set.
 
-library dart2js.test.package_root;
+library dart2js.test.missing_file;
 
 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 DiagnosticHandler, Diagnostic;
 
 import 'dart:async';
 
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirror.dart';
 
 const MEMORY_SOURCE_FILES = const {
   'main.dart': '''
 
-import 'package:foo/foo.dart';
+import 'foo.dart';
 
 main() {}
 ''',
 };
 
-void runCompiler(Uri main) {
+void runCompiler(Uri main, String expectedMessage) {
   Uri script = currentDirectory.resolve(nativeToUriPath(Platform.script));
   Uri libraryRoot = script.resolve('../../../sdk/');
 
-  MemorySourceFileProvider.MEMORY_SOURCE_FILES = MEMORY_SOURCE_FILES;
-  var provider = new MemorySourceFileProvider();
+  var provider = new MemorySourceFileProvider(MEMORY_SOURCE_FILES);
   var handler = new FormattingDiagnosticHandler(provider);
   var errors = [];
 
   void diagnosticHandler(Uri uri, int begin, int end, String message,
                          Diagnostic kind) {
     if (kind == Diagnostic.ERROR) {
       errors.add(message);
     }
     handler(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,
+  Compiler compiler = new Compiler(provider,
                                    outputProvider,
                                    diagnosticHandler,
                                    libraryRoot,
                                    null,
                                    []);
 
-  compiler.run(main);
-  Expect.equals(1, errors.length);
-  Expect.equals('Error: Cannot resolve "package:foo/foo.dart". '
-                'Package root has not been set.',
-                errors[0]);
+  asyncTest(() => compiler.run(main).then((_) {
+    Expect.equals(1, errors.length);
+    Expect.equals(expectedMessage,
+                  errors[0]);
+  }));
 }
 
 void main() {
-  runCompiler(Uri.parse('memory:main.dart'));
-  runCompiler(Uri.parse('package:foo/foo.dart'));
+  runCompiler(Uri.parse('memory:main.dart'),
+              "Error: Can't read 'memory:foo.dart' "
+              "(No such file memory:foo.dart).");
+  runCompiler(Uri.parse('memory:foo.dart'),
+              "Error: Can't read 'memory:foo.dart' "
+              "(No such file memory:foo.dart).");
+  runCompiler(Uri.parse('dart:foo'),
+              'Error: Library not found "dart:foo".');
 }