anchor.diff:  const int numMethodParams = 4;
   const int numClasses = 4;
   const int numExtensionMethodsPerClass = 3;
  +const int numDartTypeExtensions = 5;
   
   // Naming conventions.
   const varName = 'var';
  
positive.code:     }
    }
  
    String emitScalarVar(DartType tp, {bool isLhs = false, RhsFilter rhsFilter}) {
      // Randomly specialize interface type, unless emitting left hand side.
      if (!isLhs) tp = maybeSpecializeInterface(tp);
      // Collect all choices from globals, fields, locals, and parameters.
  
negative.code:       {RhsFilter rhsFilter}) {
      for (int i = m - 1; i >= 0; i--) {
        if (tp == methods[i].returnType) {
          methods[i].emitCall(depth + 1, rhsFilter: rhsFilter);
          return true;
        }
      }
  