[CRX] Replace localStorage in telemetry logic

In MV3, the background script is a service worker. localStorage is not
supported in service workers. Switch to storage.local instead.

Data migration is not implemented because it is not needed due to the
privacy-friendly design of the telemetry: In practice the data is reset
about every 4 weeks, when the major version of Chrome is updated.

extensions/chromium/manifest.json

@@ -10,6 +10,7 @@
     "16": "icon16.png"
   },
   "permissions": [
+    "alarms",
     "declarativeNetRequestWithHostAccess",
     "webRequest",
     "webRequestBlocking",

extensions/chromium/telemetry.js

@@ -42,8 +42,35 @@ limitations under the License.
     return;
   }
 
-  maybeSendPing();
+  // The localStorage API is unavailable in service workers. We store data in
-  setInterval(maybeSendPing, 36e5);
+  // chrome.storage.local and use this "localStorage" object to enable
+  // synchronous access in the logic.
+  const localStorage = {
+    telemetryLastTime: 0,
+    telemetryDeduplicationId: "",
+    telemetryLastVersion: "",
+  };
+
+  chrome.alarms.onAlarm.addListener(alarm => {
+    if (alarm.name === "maybeSendPing") {
+      maybeSendPing();
+    }
+  });
+  chrome.storage.session.get({ didPingCheck: false }, async items => {
+    if (items?.didPingCheck) {
+      return;
+    }
+    maybeSendPing();
+    await chrome.alarms.clear("maybeSendPing");
+    await chrome.alarms.create("maybeSendPing", { periodInMinutes: 60 });
+    chrome.storage.session.set({ didPingCheck: true });
+  });
+
+  function updateLocalStorage(key, value) {
+    localStorage[key] = value;
+    // Note: We mirror the data in localStorage because the following is async.
+    chrome.storage.local.set({ [key]: value });
+  }
 
   function maybeSendPing() {
     getLoggingPref(function (didOptOut) {
@@ -61,12 +88,20 @@ limitations under the License.
         // send more pings.
         return;
       }
+      doSendPing();
+    });
+  }
+
+  function doSendPing() {
+    chrome.storage.local.get(localStorage, items => {
+      Object.assign(localStorage, items);
+
       var lastTime = parseInt(localStorage.telemetryLastTime) || 0;
       var wasUpdated = didUpdateSinceLastCheck();
       if (!wasUpdated && Date.now() - lastTime < MINIMUM_TIME_BETWEEN_PING) {
         return;
       }
-      localStorage.telemetryLastTime = Date.now();
+      updateLocalStorage("telemetryLastTime", Date.now());
 
       var deduplication_id = getDeduplicationId(wasUpdated);
       var extension_version = chrome.runtime.getManifest().version;
@@ -104,7 +139,7 @@ limitations under the License.
       for (const c of buf) {
         id += (c >>> 4).toString(16) + (c & 0xf).toString(16);
       }
-      localStorage.telemetryDeduplicationId = id;
+      updateLocalStorage("telemetryDeduplicationId", id);
     }
     return id;
   }
@@ -119,7 +154,7 @@ limitations under the License.
     if (!chromeVersion || localStorage.telemetryLastVersion === chromeVersion) {
       return false;
     }
-    localStorage.telemetryLastVersion = chromeVersion;
+    updateLocalStorage("telemetryLastVersion", chromeVersion);
     return true;
   }