When you swap between document rendering engines, populate or redraw blame if appropriate

Summary: Depends on D19311. Ref T13105. Currently, blame only renders on the initial request. Instead, redraw blame after swapping views.

Test Plan: Swapped from "Source -> Hexdump -> Source" and "Hexdump -> Source". Saw blame on source in all cases.

Maniphest Tasks: T13105

Differential Revision: https://secure.phabricator.com/D19312