Consistently use "OS" rather than "Os" in identifiers.

lib/unittest.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.
 
 library unittest;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 
@@ skipping 37 matching lines @@
   // Since there's no Zone-scoped declarer, the test file is being run directly.
   // In order to run the tests, we set up our own Declarer via
   // [_globalDeclarer], and schedule a microtask to run the tests once they're
   // finished being defined.
   _globalDeclarer = new Declarer();
   scheduleMicrotask(() {
     var suite =
       new Suite(_globalDeclarer.tests,
             path: p.prettyUri(Uri.base),
             platform: "VM")
-      .filter(TestPlatform.vm, os: currentOsGuess);
+      .filter(TestPlatform.vm, os: currentOSGuess);
     // TODO(nweiz): Set the exit code on the VM when issue 6943 is fixed.
     new NoIoCompactReporter([suite], color: true).run();
   });
   return _globalDeclarer;
 }
 
 // TODO(nweiz): This and other top-level functions should throw exceptions if
 // they're called after the declarer has finished declaring.
 /// Creates a new test case with the given description and body.
 ///
@@ skipping 113 matching lines @@
 void setSoloTest(int id) {}
 
 @deprecated
 void enableTest(int id) {}
 
 @deprecated
 void disableTest(int id) {}
 
 @deprecated
 withTestEnvironment(callback()) => callback();