You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: browserstack.rb
    path of file: ./repos/travis-build/lib/travis/build/addons
    
    the code of the file until where you have to start completion: require 'travis/build/addons/base'
require 'net/http'
require 'json'

module Travis
  module Build
    
          def start_browserstack
            sh.echo 'Starting BrowserStack Local', ansi: :yellow
            sh.cmd "#{build_start_command(browserstack_key)}"
            browserstack_user = username.to_s
            sh.export ENV_USER, browserstack_user + "-travis", echo: true unless browserstack_user.empty?
            sh.export ENV_USERNAME, browserstack_user + "-travis", echo: true unless browserstack_user.empty?
            sh.export ENV_KEY, browserstack_key, echo: false
            sh.export ENV_LOCAL, 'true', echo: true
          end