Jump back to original place on traversing history

Summary: If I click on some file in ToC and then go back in browser history then it currently does nothing.

Test Plan: Collapsed file, jumped on it in ToC, collapsed it again, jumped to inline comment in it, went back in history.

Reviewers: alanh

Reviewed By: alanh

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D3328