Adding cache manifest
Look at HTML5 tools it enables you to preprocess the HTML element for manifest insertion. 


  HTML5 Tools is a module that allows Drupal sites to be built using
  HTML5 ... smartly.
  
  One of our goals is to provide as much support for HTML5 markup in a
  set of Tools provided by a module so that you can use this module with
  any HTML5 theme you'd like.