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

tests/standalone/io/https_server_test.dart

Index: tests/standalone/io/https_server_test.dart
diff --git a/tests/standalone/io/https_server_test.dart b/tests/standalone/io/https_server_test.dart
index fe622ea87bf646bc119d0fa552eba1233ce8624b..a574206be11e8753a66d0f805e9722090381c311 100644
--- a/tests/standalone/io/https_server_test.dart
+++ b/tests/standalone/io/https_server_test.dart
@@ -59,7 +59,7 @@ void testListenOn() {
 }
 
 void InitializeSSL() {
-  var testPkcertDatabase = Platform.script.resolve('pkcert').toFilePath();
+  var testPkcertDatabase = join(dirname(Platform.script), 'pkcert');
   SecureSocket.initialize(database: testPkcertDatabase,
                           password: 'dartdart');
 }