anchor.diff:  
     /// Starts the [Stopwatch].
     ///
  -  /// The [elapsed] count is increasing monotonically. If the [Stopwatch] has
  +  /// The [elapsed] count increases monotonically. If the [Stopwatch] has
     /// been stopped, then calling start again restarts it without resetting the
     /// [elapsed] count.
     ///
  
positive.code: 
  part of dart.core;
  
  /// A simple stopwatch interface to measure elapsed time.
  class Stopwatch {
    /// Cached frequency of the system in Hz (ticks per second).
    ///
  
negative.code:   /// The following example shows how to start a [Stopwatch]
    /// immediately after allocation.
    /// ```dart
    /// final stopwatch = Stopwatch()..start();
    /// ```
    Stopwatch() {
      _frequency; // Ensures initialization before using any method.
  