transformStatements_(statements) {
    this.tempVarStack_.push(new VarScope(this.options));

    let transformedStatements = this.transformList(statements);

    let vars = this.tempVarStack_.pop();
    if (vars.isEmpty())
      return transformedStatements;

    let variableStatement = vars.createVariableStatement();
    vars.release(this);

    return prependStatements(transformedStatements, variableStatement);
  }
Transforms a an array of statements and adds a new temp var scope.
@param {Array.<ParseTree>} statements
@return {Array.<ParseTree>}
@private