title: Firebase messaging on android and permissions
body: <p>I recently added firebase messaging to my android app and I noticed some new permissions required to my app at similar time, for example:
  <code>android.permission.READ_PHONE_STATE</code>
  I couldn't find anywhere in documentation, why is this permission required. I even tried to explicitly disable it in manifest (<code>tools:node="remove"</code>) and messaging still works for me. It's kinda messy and I want to use only as few permissions as I need for sake of my users.</p>
  
  <p>Is this permissions really needed by messaging or is it added automatically from one of library dependencies?
  How can I tell what permissions is being added by what? I tried <code>manifest-merger-report.txt</code>, but there was no mention about <code>READ_PHONE_STATE</code>.</p>
  
  <p>Thanks!</p>