fix: use powerMonitor.on() only after app is ready

powerMonitor can't be used until the app is ready; however, on Linux,
powerMonitor.on() was called as soon as lib/browser/api/power-monitor.ts
was loaded.

This patch takes @vladimiry's suggestion of wrapping that in an
app.on('ready') handler to prevent powerMonitor.on() from being called
prematurely.

Fixes #21716

lib/browser/api/power-monitor.ts

@@ -10,18 +10,28 @@ Object.setPrototypeOf(PowerMonitor.prototype, EventEmitter.prototype)
 
 const powerMonitor = createLazyInstance(createPowerMonitor, PowerMonitor, true)
 
-// On Linux we need to call blockShutdown() to subscribe to shutdown event.
 if (process.platform === 'linux') {
-  powerMonitor.on('newListener', (event:string) => {
-    if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
-      powerMonitor.blockShutdown()
-    }
-  })
-
-  powerMonitor.on('removeListener', (event: string) => {
-    if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
-      powerMonitor.unblockShutdown()
-    }
+  /* In order to delay system shutdown when e.preventDefault() is invoked
+   * on a powerMonitor 'shutdown' event, we need an org.freedesktop.login1
+   * delay lock. For more details see the "Taking Delay Locks" section of
+   * https://www.freedesktop.org/wiki/Software/systemd/inhibit/
+   *
+   * So here we watch for 'shutdown' listeners to be added or removed and
+   * set or unset our shutdown delay lock accordingly. */
+  const { app } = require('electron')
+  app.once('ready', (): void => {
+    powerMonitor.on('newListener', (event: string) => {
+      // if first shutdown listener added
+      if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
+        powerMonitor.blockShutdown()
+      }
+    })
+    powerMonitor.on('removeListener', (event: string) => {
+      // if last shutdown listener removed
+      if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
+        powerMonitor.unblockShutdown()
+      }
+    })
   })
 }