code: private void changeMethodSignature(ImmutableSortedMap<Integer, String> argNames, Node paramList) {
      ImmutableSortedMap<Integer, String> newParams = argNames.tailMap(paramList.getChildCount());
      for (String name : newParams.values()) {
        paramList.addChildToBack(IR.name(name).useSourceInfoIfMissingFrom(paramList));
      }
      if (!newParams.isEmpty()) {
        compiler.reportChangeToEnclosingScope(paramList);
      }
    }
docs: Inserts new formal parameters into the method's signature based on the given set of names.
  
  <p>Example: function() --> function(r0, r1, r2)
  
  @param argNames maps param index to param name, if the param with that index has a name.
  @param paramList node representing the function signature