anchor.diff:    /// The following example shows how to start a [Stopwatch]
     /// immediately after allocation.
     /// ```dart
  -  /// var stopwatch = Stopwatch()..start();
  +  /// final stopwatch = Stopwatch()..start();
     /// ```
     Stopwatch() {
       _frequency; // Ensures initialization before using any method.
  
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: 
    /// Starts the [Stopwatch].
    ///
    /// The [elapsed] count increases monotonically. If the [Stopwatch] has
    /// been stopped, then calling start again restarts it without resetting the
    /// [elapsed] count.
    ///
  