Add extra metrics to the budget (#3484)

lib/plugins/budget/verify.js

@@ -131,6 +131,32 @@ module.exports = {
               log.error(`Could not find the user timing ${metric}`);
               continue;
             }
+          } else if (metricType === 'extras' && tool === 'browsertime') {
+            const budgetValue = budgetForThisURL[metricType][metric];
+            const value = get(
+              message.data,
+              'statistics.extras.' + metric + '.median'
+            );
+            if (value) {
+              const item = getItem(
+                { name: metric, format: time.ms },
+                metricType,
+                metric,
+                value,
+                budgetValue,
+                'max'
+              );
+              if (value > budgetValue) {
+                item.status = 'failing';
+                failing.push(item);
+              } else {
+                working.push(item);
+              }
+              continue;
+            } else {
+              log.error(`Could not find the extra metric ${metric}`);
+              continue;
+            }
           }
         }
       }