anchor.diff:      }
       return new VariableModel<Variable, Type>(
           null, tested, assigned, false, writeCaptured);
  -  }
  -
  -  /// Returns a new [VariableModel] reflecting the fact that the variable was
  -  /// just initialized.
  -  VariableModel<Variable, Type> initialize() {
  -    if (promotedTypes == null && tested.isEmpty && assigned && !unassigned) {
  -      return this;
  -    }
  -    return new VariableModel<Variable, Type>(
  -        null, const [], true, false, writeCaptured);
     }
   
     /// Returns an updated model reflect a control path that is known to have
  
positive.code: 
    /// Creates a [VariableModel] representing a variable that's never been seen
    /// before.
    VariableModel.fresh()
        : promotedTypes = null,
          tested = const [],
          assigned = false,
          unassigned = true,
          writeCaptured = false;
  
    /// Returns a new [VariableModel] in which any promotions present have been
  
negative.code:         );
  
    @visibleForTesting
    FlowModel.withInfo(this.reachable, this.variableInfo) {
      assert(reachable != null);
      assert(() {
        for (VariableModel<Variable, Type> value in variableInfo.values) {
  