- Fix more bad uses of Platform.packageRoot.

tests/compiler/dart2js/incremental/hello_test.dart

 // Copyright (c) 2014, 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 a sequence of modifications to hello-world which used to cause problems
 // on Try Dart.
 
 import 'dart:io' show
     Platform;
 
@@ skipping 67 matching lines @@
 var testResults = {
   '/test1.dart': true,
   '/test2.dart': true,
   '/test3.dart': false,
   '/test4.dart': false,
   '/test5.dart': true,
 };
 
 main() {
   Uri libraryRoot = Uri.base.resolve('sdk/');
-  Uri packageRoot = Uri.base.resolveUri(
-      new Uri.file('${Platform.packageRoot}/'));
+  Uri packageRoot = Uri.base.resolve(Platform.packageRoot);
   MemorySourceFileProvider provider =
       new MemorySourceFileProvider(tests);
   asyncTest(() => runTests(libraryRoot, packageRoot, provider));
 }
 
 Future runTests(
     Uri libraryRoot,
     Uri packageRoot,
     MemorySourceFileProvider provider) {
   IncrementalCompiler compiler = new IncrementalCompiler(
@@ skipping 16 matching lines @@
 
 void handler(Uri uri,
              int begin,
              int end,
              String message,
              Diagnostic kind) {
   if (kind != Diagnostic.VERBOSE_INFO) {
     print('$uri:$begin:$end:$message:$kind');
   }
 }