Update app and tooling

node_modules/web-vitals/src/lib/getFirstHidden.ts

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {onHidden} from './onHidden.js';
+
+
+let firstHiddenTime: number
+
+export const getFirstHidden = () => {
+  if (firstHiddenTime === undefined) {
+    // If the document is hidden when this code runs, assume it was hidden
+    // since navigation start. This isn't a perfect heuristic, but it's the
+    // best we can do until an API is available to support querying past
+    // visibilityState.
+    firstHiddenTime = document.visibilityState === 'hidden' ? 0 : Infinity;
+
+    // Update the time if/when the document becomes hidden.
+    onHidden(({timeStamp}) => firstHiddenTime = timeStamp, true);
+  }
+
+  return {
+    get timeStamp() {
+      return firstHiddenTime;
+    }
+  }
+};