Load default site theme if provided

Change-Id: Ic0b691aafa35abbaf293099634d652c01e703456

polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.js

@@ -31,6 +31,11 @@
     _configChanged(config) {
       const jsPlugins = config.js_resource_paths || [];
       const htmlPlugins = config.html_resource_paths || [];
+      const defaultTheme = config.default_theme;
+      if (defaultTheme) {
+        // Make theme first to be first to load.
+        htmlPlugins.unshift(defaultTheme);
+      }
       Gerrit._setPluginsCount(jsPlugins.length + htmlPlugins.length);
       this._loadJsPlugins(jsPlugins);
       this._importHtmlPlugins(htmlPlugins);
@@ -62,7 +67,10 @@
       if (pathOrUrl.startsWith('http')) {
         return pathOrUrl;
       }
-      return this.getBaseUrl() + '/' + pathOrUrl;
+      if (!pathOrUrl.startsWith('/')) {
+        pathOrUrl = '/' + pathOrUrl;
+      }
+      return this.getBaseUrl() + pathOrUrl;
     },
   });
 })();

polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host_test.html

@@ -131,5 +131,16 @@ limitations under the License.
       assert.isTrue(element._createScriptTag.calledWith(
           'https://example.com/baz'));
     });
+
+    test('default theme is loaded with html plugins', () => {
+      element.config = {
+        default_theme: '/oof',
+        html_resource_paths: ['some'],
+      };
+      assert.isTrue(element.importHref.calledWith(
+          '/oof', Gerrit._pluginInstalled, Gerrit._pluginInstalled, true));
+      assert.isTrue(element.importHref.calledWith(
+          '/some', Gerrit._pluginInstalled, Gerrit._pluginInstalled, true));
+    });
   });
 </script>