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

tests/standalone/io/http_proxy_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:crypto/crypto.dart";
 import "package:expect/expect.dart";
 import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 import 'dart:convert';
@@ skipping 728 matching lines @@
               server.shutdown();
               client.close();
             }
           });
         });
     }
   });
 }
 
 void InitializeSSL() {
-  var testPkcertDatabase = Platform.script.resolve('pkcert').toFilePath();
+  var testPkcertDatabase = join(dirname(Platform.script), 'pkcert');
   SecureSocket.initialize(database: testPkcertDatabase,
                           password: 'dartdart');
 }
 
 main() {
   InitializeSSL();
   testInvalidProxy();
   testDirectProxy();
   testProxy();
   testProxyChain();
   testProxyFromEnviroment();
   // The two invocations of uses the same global variable for state -
   // run one after the other.
   testProxyAuthenticate(false)
       .then((_) => testProxyAuthenticate(true));
   // This test is not normally run. It can be used for locally testing
   // with a real proxy server (e.g. Apache).
   //testRealProxy();
   //testRealProxyAuth();
 }