Change dart:io Platform.script to return a URI. Change all uses of Platform.script to work with th…

tests/compiler/dart2js/mirror_tree_shaking_test.dart

Index: tests/compiler/dart2js/mirror_tree_shaking_test.dart
diff --git a/tests/compiler/dart2js/mirror_tree_shaking_test.dart b/tests/compiler/dart2js/mirror_tree_shaking_test.dart
index 67717f64d024a825af65b08a526e8e7c7a384bff..5104a482a8354622b8f7afe28349990afae13aed 100644
--- a/tests/compiler/dart2js/mirror_tree_shaking_test.dart
+++ b/tests/compiler/dart2js/mirror_tree_shaking_test.dart
@@ -17,7 +17,7 @@ import '../../../sdk/lib/_internal/compiler/compiler.dart'
 import 'dart:async';
 
 main() {
-  Uri script = currentDirectory.resolve(nativeToUriPath(Platform.script));
+  Uri script = currentDirectory.resolveUri(Platform.script);
   Uri libraryRoot = script.resolve('../../../sdk/');
   Uri packageRoot = script.resolve('./packages/');