my_activity: search gerrit review too

This is where PolyGerrit & repo & other Gerrit CLs land.

Change-Id: If584cfce7d6e78f01e30531e5eee70a51a354164
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2079413
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>

my_activity.py

@@ -75,6 +75,9 @@ gerrit_instances = [
     'shorturl': 'r.android.com',
     'short_url_protocol': 'https',
   },
+  {
+    'url': 'gerrit-review.googlesource.com',
+  },
   {
     'url': 'chrome-internal-review.googlesource.com',
     'shorturl': 'crrev.com/i',