Stubbing PerformanceObserver in tests

spec/frontend/environment.js

@@ -58,6 +58,14 @@ class CustomEnvironment extends JSDOMEnvironment {
       measure: () => null,
       getEntriesByName: () => [],
     });
+
+    this.global.PerformanceObserver = class {
+      /* eslint-disable no-useless-constructor, no-unused-vars, no-empty-function, class-methods-use-this */
+      constructor(callback) {}
+      disconnect() {}
+      observe(element, initObject) {}
+      /* eslint-enable no-useless-constructor, no-unused-vars, no-empty-function, class-methods-use-this */
+    };
   }
 
   async teardown() {