Embedding Google Analytics code on CiviMail message
This doesn't seem to be supported yet, but thanks for asking - giving voice to needs is how these things start!

Currently CiviMail generates a URL like  http://dmaster.demo.civicrm.org/civicrm/mailing/view?reset=1&amp;id=10 which renders the mail as sent out (without site theme).

First thought: look at using your existing site theme to include your tracking codes, and display your newsletter content wrapped in the default site theme. This might be possible by commenting out the CRM_Utils_System ::civiExit() line mentioned in @diegov's answer below, or by (eg) creating a Drupal View which displays the rendered Mailing content at a similar path but without skipping the site theme.

Alternatively, a quick CiviCRM extension could detect the mail when viewed over the web and include your tracking codes?

Both of these would require some work, so consider contributing the end result back to the community if you do take it from here! And if you can't, maybe post it as a feature request on issues.civicrm.org?