fix(gerrit): return HTML titles in more cases

At present, we don't return HTML titles if there's a trailing slash,
or a patchset. Instead, just consume the / and anything after it.

This also fixes /123, because this is HTTP redirected to the full path
*with a trailing slash* which otherwise wouldn't get the title
injected.

Change-Id: Idfd0e67752880a37dce0b400a3c1cfc53fac2912
Reviewed-on: https://cl.tvl.fyi/c/depot/+/859
Reviewed-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

third_party/gerrit/0002-Syntax-highlight-nix.patch

@@ -0,0 +1,24 @@
+From f14cba31f2a9a75d06e58fd6313cc60d0cf5e690 Mon Sep 17 00:00:00 2001
+From: Luke Granger-Brown <git@lukegb.com>
+Date: Thu, 2 Jul 2020 23:02:32 +0100
+Subject: [PATCH 2/4] Syntax highlight nix
+
+---
+ .../app/elements/diff/gr-syntax-layer/gr-syntax-layer.js         | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.js b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.js
+index f1e930f177..cc937cff67 100644
+--- a/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.js
++++ b/polygerrit-ui/app/elements/diff/gr-syntax-layer/gr-syntax-layer.js
+@@ -101,6 +101,7 @@ const LANGUAGE_MAP = {
+   'text/x-vhdl': 'vhdl',
+   'text/x-yaml': 'yaml',
+   'text/vbscript': 'vbscript',
++  'application/x-mix-transfer': 'nix',
+ };
+ const ASYNC_DELAY = 10;
+ 
+-- 
+2.25.1
+