Fix keyboard navigation regressions in the diff viewer.
Review Request #9112 — Created July 31, 2017 and submitted
A recent change improved performance in the diff viewer by optimizing
selectors. One of the selectors optimized was the one used to find
anchors in a diff. Unfortunately, it only looked in
<thead>, skipping the file anchors. This prevented these
anchors from navigating to file headers, and for review requests
containing newly-introduced files, it wasn't possible to navigate to the
This change fixes the selector and adds a new suite of tests to ensure
that anchor loading, navigation, and key bindings all work correctly.
Tested manually that diff navigation worked for all diffs I threw at it.
Unit tests pass.