Rename StopWatch to Stopwatch. Add new Stopwatch.start() and Stopwatch.reset().

frog/world.dart

 // Copyright (c) 2011, 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.
 
 /** The one true [World]. */
 World world;
 
 /**
  * Should be called exactly once to setup singleton world.
  * Can use world.reset() to reinitialize.
@@ skipping 419 matching lines @@
     } else {
       if (warnings > 0) {
         info('compilation completed successfully with $warnings warnings');
       } else {
         info('compilation completed sucessfully');
       }
     }
   }
 
   withTiming(String name, f()) {
-    final sw = new StopWatch();
+    final sw = new Stopwatch();
     sw.start();
     var result = f();
     sw.stop();
     info('$name in ${sw.elapsedInMs()}msec');
     return result;
   }
 }