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/0003-Syntax-highlight-rules.pl.patch

@@ -0,0 +1,44 @@
+From c3603950e5ae377514febbebf9aa26c31e07cd5d Mon Sep 17 00:00:00 2001
+From: Luke Granger-Brown <git@lukegb.com>
+Date: Thu, 2 Jul 2020 23:02:43 +0100
+Subject: [PATCH 3/4] Syntax highlight rules.pl
+
+---
+ .../elements/diff/gr-syntax-layer/gr-syntax-layer.js   | 10 ++++++++++
+ 1 file changed, 10 insertions(+)
+
+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 cc937cff67..2145bc169b 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
+@@ -105,6 +105,10 @@ const LANGUAGE_MAP = {
+ };
+ const ASYNC_DELAY = 10;
+ 
++const FILENAME_OVERRIDES = {
++  'rules.pl': 'prolog',
++};
++
+ const CLASS_WHITELIST = {
+   'gr-diff gr-syntax gr-syntax-attr': true,
+   'gr-diff gr-syntax gr-syntax-attribute': true,
+@@ -236,10 +240,16 @@ class GrSyntaxLayer extends GestureEventListeners(
+     }
+   }
+ 
++  _basename(filename) {
++    const pieces = filename.split(/\//);
++    return pieces[pieces.length-1];
++  }
++
+   _getLanguage(diffFileMetaInfo) {
+     // The Gerrit API provides only content-type, but for other users of
+     // gr-diff it may be more convenient to specify the language directly.
+     return diffFileMetaInfo.language ||
++        FILENAME_OVERRIDES[this._basename(diffFileMetaInfo.name)] ||
+         LANGUAGE_MAP[diffFileMetaInfo.content_type];
+   }
+ 
+-- 
+2.25.1
+