Add Stopwatch.isRunning.

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 {
@@ skipping 45 matching lines @@
 
   /**
    * 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 {
-      if (_stop == null) {
-        return;
-      }
-      // Restarting this stopwatch. Prepend the elapsed time to the current
+      // Restart this stopwatch. Prepend the elapsed time to the current
       // start time.
       _start = _now() - (_stop - _start);
       _stop = null;
     }
   }
 
   void stop() {
-    if (_start == null || _stop != null) {
-      return;
-    }
+    if (!isRunning) return;
     _stop = _now();
   }
 
   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
@@ skipping 12 matching lines @@
   int get elapsedMicroseconds {
     return (elapsedTicks * 1000000) ~/ frequency;
   }
 
   int get elapsedMilliseconds {
     return (elapsedTicks * 1000) ~/ frequency;
   }
 
   int get frequency => _frequency();
 
+  bool get isRunning => _start != null && _stop == null;
+
   external static int _frequency();
   external static int _now();
 }