- Fix or simplify use of Platform.packageRoot.

tests/compiler/dart2js/mirrors/mirrors_test_helper.dart

Index: tests/compiler/dart2js/mirrors/mirrors_test_helper.dart
diff --git a/tests/compiler/dart2js/mirrors/mirrors_test_helper.dart b/tests/compiler/dart2js/mirrors/mirrors_test_helper.dart
index 0aa116f492c5bd6f2a739a42c9c8b2e2003b7389..c308daede151c8bbf8d0be083315192d1a5e4d27 100644
--- a/tests/compiler/dart2js/mirrors/mirrors_test_helper.dart
+++ b/tests/compiler/dart2js/mirrors/mirrors_test_helper.dart
@@ -24,8 +24,7 @@ Future<MirrorSystem> analyze(String test) {
 Future<MirrorSystem> analyzeUri(Uri testUri) {
   Uri repository = Platform.script.resolve('../../../../');
   Uri libraryRoot = repository.resolve('sdk/');
-  Uri packageRoot = Uri.base.resolveUri(
-      new Uri.file('${Platform.packageRoot}/'));
+  Uri packageRoot = Uri.base.resolve(Platform.packageRoot);
   var provider = new CompilerSourceFileProvider();
   var handler = new FormattingDiagnosticHandler(provider);
   return source_mirrors.analyze(
@@ -34,4 +33,4 @@ Future<MirrorSystem> analyzeUri(Uri testUri) {
       packageRoot,
       provider,
       handler);
-}
+}