Change Platform members to getters instead of methods.

tests/standalone/io/dart_std_io_pipe_test.dart

 // Copyright (c) 2012, 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.
 //
 // Test a dart sub-process handling stdio with different types of
 // redirection.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
@@ skipping 61 matching lines @@
 
   process.onError = (ProcessException error) {
     Expect.fail(error.toString());
   };
 }
 
 // This tests that the Dart standalone VM can handle piping to stdin
 // and can pipe to stdout.
 main() {
   // Don't try to run shell scripts on Windows.
-  var os = Platform.operatingSystem();
+  var os = Platform.operatingSystem;
   if (os == 'windows') return;
 
   // Get the shell script for testing the Standalone Dart VM with
   // piping and redirections of stdio.
   var shellScript = new File("tests/standalone/io/dart_std_io_pipe_test.sh");
   if (!shellScript.existsSync()) {
     shellScript = new File("../tests/standalone/io/dart_std_io_pipe_test.sh");
   }
   // Get the Dart script file which echoes stdin to stdout or stderr or both.
   var scriptFile = new File("tests/standalone/io/process_std_io_script.dart");
   if (!scriptFile.existsSync()) {
     scriptFile = new File("../tests/standalone/io/process_std_io_script.dart");
   }
 
   // Run the shell script.
   test(shellScript.name, scriptFile.name, "0");
   test(shellScript.name, scriptFile.name, "1");
   test(shellScript.name, scriptFile.name, "2");
 }