code: function getLexicalBindingNames(tree) {
    let names = new StringSet();
    if (tree !== null && tree.type === VARIABLE_DECLARATION_LIST &&
        tree.declarationType !== VAR) {
      let visitor = new FindNames(names);
      for (let i = 0; i < tree.declarations.length; i++) {
        visitor.visitAny(tree.declarations[i].lvalue);
      }
    }
    return names;
  }
docs: Gets the variable names in a declaration list. This is used to get the names
  from for loops (for, for-in and for-of)
  @param {VariableDeclarationList} tree
  @return {StringSet} An object as a map where the keys are the variable names.