Get entire page content (generated HTML in browser)

You can use output buffering to accomplish this.

Add a high priority hook directly before the template is rendered:

add_action('template_redirect', 'foo_buffer_go', 0);
function foo_buffer_go(){
    ob_start('foo_buffer_callback');
}

Add a shutdown hook with an extremely low priority.

add_action('shutdown', 'foo_buffer_stop', 1000);
function foo_buffer_stop(){
    ob_end_flush();
}

Inside your callback, you manipulate the rendered HTML.

function foo_buffer_callback($buffer){
  //Do something with the buffer (HTML)
  return $buffer;
}

You may download this as a plugin here: http://3-3.me/B9lK

1. Enable the plugin
2. Visit the site and it will be rendered as “Foo Bar” which means you are capturing the entirety of the generated HTML