Build Observatory as part of runtime

runtime/observatory/lib/tracer.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 tracer;
 
 import 'dart:async';
 
 import 'package:logging/logging.dart';
 import 'package:observe/observe.dart';
@@ skipping 77 matching lines @@
     _time.reset();
     events.clear();
   }
 
   TraceEvent trace(String message, {Map map: null}) {
     var event = new TraceEvent.msg(_time.elapsedMicroseconds, message, map);
     events.add(event);
     return event;
   } 
 }