title: Optionally inject Content Script
body: <p>Content Script can be injected programatically or permanently by declaring in Extension manifest file. Programatic injection require host permission, which is generally grant by browser or page action.</p>
  
  <p>In my use case, I want to inject gmail, outlook.com and yahoo mail web site without user action. I can do by declaring all of them manifest, but by doing so require all data access to those account. Some use may want to grant only outlook.com, but not gmail. Programatic injection does not work because I need to know when to inject. Using tabs permission is also require another permission.</p>
  
  <p>Is there any good way to optionally inject web site?  </p>