Change dart:io Platform.script to return a Uri.

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.missing_file;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 13 matching lines @@
 const MEMORY_SOURCE_FILES = const {
   'main.dart': '''
 
 import 'foo.dart';
 
 main() {}
 ''',
 };
 
 void runCompiler(Uri main, String expectedMessage) {
-  Uri script = currentDirectory.resolve(nativeToUriPath(Platform.script));
+  Uri script = currentDirectory.resolveUri(Platform.script);
   Uri libraryRoot = script.resolve('../../../sdk/');
 
   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);
@@ skipping 24 matching lines @@
 void main() {
   runCompiler(Uri.parse('memory:main.dart'),
               "Error: Can't read 'memory:foo.dart' "
               "(Exception: No such file memory:foo.dart).");
   runCompiler(Uri.parse('memory:foo.dart'),
               "Error: Can't read 'memory:foo.dart' "
               "(Exception: No such file memory:foo.dart).");
   runCompiler(Uri.parse('dart:foo'),
               "Error: Library not found 'dart:foo'.");
 }