Noteworthy decisions:
- Preferences are hidden when diff prefs are not loaded or the user is not
logged in.
- Preferences are hidden on small screens
- The trigger button is in gr-change-view but the gr-diff-preferences
is part of gr-file-list. This is because gr-file-list because diff
preferences and local preferences are more closely tied with that
than the change view. In order to put it in the change view, local
prefs would also have to be two-way bound back.
Also fixes computePrefsButtonHidden in gr-diff-view as well. The
function did not work as intended before. If preferences didn't exist,
the function would not get called, and the container would not be
hidden.
Bug: Issue 5426
Change-Id: I361cdf132c6e15b5ae2f15e62af318cfa05161ce