Change Platform members to getters instead of methods.

tests/standalone/io/process_test_util.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.
 
 String getPlatformOutDir() {
-  var os = Platform.operatingSystem();
+  var os = Platform.operatingSystem;
   if (os == 'linux') return 'out/';
   if (os == 'macos') return 'xcodebuild/';
   return '';  // Windows.
 }
 
 String getPlatformExecutableExtension() {
-  var os = Platform.operatingSystem();
+  var os = Platform.operatingSystem;
   if (os == 'windows') return '.exe';
   return '';  // Linux and Mac OS.
 }
 
 String getProcessTestFileName() {
   var outDir = getPlatformOutDir();
   var extension = getPlatformExecutableExtension();
   // We do not expose information about the mode or architecture we are testing
   // to the tests themselves, so we use any working copy.
   var names = ['${outDir}Release_ia32/process_test$extension',
@@ skipping 19 matching lines @@
                '${outDir}Release_x64/dart$extension',
                '${outDir}Debug_x64/dart$extension'];
 
   for (var name in names) {
     if (new File(name).existsSync()) {
       return name;
     }
   }
   Expect.fail('Could not find the dart executable.');
 }