Package-ify Dromaeo and browser controller functionality

samples/third_party/dromaeo/web/common/Interval.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.
 
 part of common;
 
 // A utility object for measuring time intervals.
 
 class Interval {
   int _start, _stop;
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   // Microseconds from between start() and stop().
   int get elapsedMicrosec {
     return (_stop - _start) * 1000;
   }
 
   // Milliseconds from between start() and stop().
   int get elapsedMillisec {
     return (_stop - _start);
   }
 }