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

tests/standalone/io/process_shell_test.dart

Index: tests/standalone/io/process_shell_test.dart
diff --git a/tests/standalone/io/process_shell_test.dart b/tests/standalone/io/process_shell_test.dart
index 4e6593d4605f70b8bba13ab45822e3f9b66009d2..91442fea2fc0a5840d7ea9c7ed6ebc734805c220 100644
--- a/tests/standalone/io/process_shell_test.dart
+++ b/tests/standalone/io/process_shell_test.dart
@@ -11,7 +11,7 @@ import "dart:isolate";
 void testRunShell() {
   test(args) {
     asyncStart();
-    var path = join(dirname(Platform.script), "process_echo_util.dart");
+    var path = Platform.script.resolve("process_echo_util.dart").toFilePath();
     Process.run(Platform.executable,
                 [path]..addAll(args),
                 runInShell: true)