Add a 'checks--combined' URL parameter to 'changes' queries

As a first step this parameter is always added, because the server will
ignore it, if the checks plugin is not installed.

Change-Id: I576e53c5b975f2cbc9ef3cdb741eaad072c779a9
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js
index e69c8fc..6ae75ee 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js
@@ -1260,6 +1260,17 @@
         O: options,
         S: opt_offset || 0,
       };
+
+      // This triggers a CheckChangeInfo entity to be added to the plugins
+      // list in ChangeInfo, if the checks plugin is installed. Otherwise the
+      // server will just ignore this.
+      // TODO(brohlfs): Only add this parameter, if the checks plugin is
+      // installed. Currently this code may be executed even before the
+      // /config/server/info response is processed, so having that information
+      // included in the host page is a blocking requirement for resolving this
+      // TODO.
+      params['checks--combined'] = '';
+
       if (opt_changesPerPage) { params.n = opt_changesPerPage; }
       if (opt_query && opt_query.length > 0) {
         params.q = opt_query;