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

tests/standalone/io/platform_test.dart

Index: tests/standalone/io/platform_test.dart
diff --git a/tests/standalone/io/platform_test.dart b/tests/standalone/io/platform_test.dart
index 04494aac90cbc3dd8d4ca174519f65490ae0a738..85a7a4713ad3bb13dda7a64db72b8820ab799069 100644
--- a/tests/standalone/io/platform_test.dart
+++ b/tests/standalone/io/platform_test.dart
@@ -25,7 +25,7 @@ test() {
   var environment = Platform.environment;
   Expect.isTrue(environment is Map<String, String>);
   Expect.isTrue(Platform.executable.contains('dart'));
-  Expect.isTrue(Platform.script.replaceAll('\\', '/').
+  Expect.isTrue(Platform.script.path.
                 endsWith('tests/standalone/io/platform_test.dart'));
   Directory packageRoot = new Directory(Platform.packageRoot);
   Expect.isTrue(packageRoot.existsSync());
@@ -48,7 +48,7 @@ testIsolate() {
   port.first.then((results) {
     Expect.equals(Platform.executable, results["Platform.executable"]);
 
-    Uri uri = new Uri.file(results["Platform.script"]);
+    Uri uri = results["Platform.script"];
     // SpawnFunction retains the script url of the parent which in this
     // case was a relative path.
     Expect.equals("file", uri.scheme);