Remove Stopwatch interface and make it a class.

sdk/lib/core/stopwatch.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 dart.core;
 
 /**
  * A simple [Stopwatch] interface to measure elapsed time.
  */
-abstract class Stopwatch {
+class Stopwatch {
+  // The _start and _stop fields capture the time when [start] and [stop]
+  // are called respectively.
+  // If _start is null, then the [Stopwatch] has not been started yet.
+  // If _stop is null, then the [Stopwatch] has not been stopped yet,
+  // or is running.
+  int _start;
+  int _stop;
+
   /**
    * Creates a [Stopwatch] in stopped state with a zero elapsed count.
    *
    * The following example shows how to start a [Stopwatch]
    * right after allocation.
    *
    *     Stopwatch stopwatch = new Stopwatch()..start();
    */
-  factory Stopwatch() => new _StopwatchImpl();
+  Stopwatch() : _start = null, _stop = null {}
 
   /**
    * Starts the [Stopwatch]. The [elapsed] count is increasing monotonically.
    * If the [Stopwatch] has been stopped, then calling start again restarts it
    * without resetting the [elapsed] count.
    * If the [Stopwatch] is currently running, then calling start does nothing.
    */
-  void start();
-
-  /**
-   * Stops the [Stopwatch]. The [elapsed] count stops increasing.
-   * If the [Stopwatch] is currently not running, then calling stop does
-   * nothing.
-   */
-  void stop();
-
-  /**
-   * Resets the [elapsed] count to zero. This method does not stop or start
-   * the [Stopwatch].
-   */
-  void reset();
-
-  /**
-   * Returns the elapsed number of clock ticks since calling [start] while the
-   * [Stopwatch] is running.
-   * Returns the elapsed number of clock ticks between calling [start] and
-   * calling [stop].
-   * Returns 0 if the [Stopwatch] has never been started.
-   * The elapsed number of clock ticks increases by [frequency] every second.
-   */
-  int get elapsedTicks;
-
-  /**
-   * Returns the [elapsedTicks] counter converted to microseconds.
-   */
-  int get elapsedMicroseconds;
-
-  /**
-   * Returns the [elapsedTicks] counter converted to milliseconds.
-   */
-  int get elapsedMilliseconds;
-
-  /**
-   * Returns the frequency of the elapsed counter in Hz.
-   */
-  int get frequency;
-
-  /**
-   * Returns wether the [StopWatch] is currently running.
-   */
-  bool get isRunning;
-}
-
-class _StopwatchImpl implements Stopwatch {
-  // The _start and _stop fields capture the time when [start] and [stop]
-  // are called respectively.
-  // If _start is null, then the [Stopwatch] has not been started yet.
-  // If _stop is null, then the [Stopwatch] has not been stopped yet,
-  // or is running.
-  int _start;
-  int _stop;
-
-  _StopwatchImpl() : _start = null, _stop = null {}
-
   void start() {
     if (isRunning) return;
     if (_start == null) {
       // This stopwatch has never been started.
       _start = _now();
     } else {
       // Restart this stopwatch. Prepend the elapsed time to the current
       // start time.
       _start = _now() - (_stop - _start);
       _stop = null;
     }
   }
 
+  /**
+   * Stops the [Stopwatch]. The [elapsed] count stops increasing.
+   * If the [Stopwatch] is currently not running, then calling stop does
+   * nothing.
+   */
   void stop() {
     if (!isRunning) return;
     _stop = _now();
   }
 
+  /**
+   * Resets the [elapsed] count to zero. This method does not stop or start
+   * the [Stopwatch].
+   */
   void reset() {
     if (_start == null) return;
     // If [_start] is not null, then the stopwatch had already been started. It
     // may running right now.
     _start = _now();
     if (_stop != null) {
       // The watch is not running. So simply set the [_stop] to [_start] thus
       // having an elapsed time of 0.
       _stop = _start;
     }
   }
 
+  /**
+   * Returns the elapsed number of clock ticks since calling [start] while the
+   * [Stopwatch] is running.
+   * Returns the elapsed number of clock ticks between calling [start] and
+   * calling [stop].
+   * Returns 0 if the [Stopwatch] has never been started.
+   * The elapsed number of clock ticks increases by [frequency] every second.
+   */
   int get elapsedTicks {
     if (_start == null) {
       return 0;
     }
     return (_stop == null) ? (_now() - _start) : (_stop - _start);
   }
 
+  /**
+   * Returns the [elapsedTicks] counter converted to microseconds.
+   */
   int get elapsedMicroseconds {
     return (elapsedTicks * 1000000) ~/ frequency;
   }
 
+  /**
+   * Returns the [elapsedTicks] counter converted to milliseconds.
+   */
   int get elapsedMilliseconds {
     return (elapsedTicks * 1000) ~/ frequency;
   }
 
+  /**
+   * Returns the frequency of the elapsed counter in Hz.
+   */
   int get frequency => _frequency();
 
+  /**
+   * Returns wether the [StopWatch] is currently running.
+   */
   bool get isRunning => _start != null && _stop == null;
 
   external static int _frequency();
   external static int _now();
 }