Add 'pageId', 'revisionId', 'action' and 'isAnon'

We'd like to be able to attribute page performance to user action and
page content, so log them when available. Also log whether or not the
user was logged in, since caching behavior is contingent on it.

Change-Id: I087f2647e5aa1aa0a9535bf3dc0bfcfca646d72f