Simplify the public PowerObserver interface

lib/browser/api/power-monitor.js

@@ -5,16 +5,19 @@ const {powerMonitor, PowerMonitor} = process.atomBinding('power_monitor')
 Object.setPrototypeOf(PowerMonitor.prototype, EventEmitter.prototype)
 EventEmitter.call(powerMonitor)
 
-powerMonitor.on('newListener', (event) => {
-  if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
-    powerMonitor.blockShutdown()
-  }
-})
+// On Linux we need to call blockShutdown() to subscribe to shutdown event.
+if (process.platform === 'linux') {
+  powerMonitor.on('newListener', (event) => {
+    if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
+      powerMonitor.blockShutdown()
+    }
+  })
 
-powerMonitor.on('removeListener', (event) => {
-  if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
-    powerMonitor.unblockShutdown()
-  }
-})
+  powerMonitor.on('removeListener', (event) => {
+    if (event === 'shutdown' && powerMonitor.listenerCount('shutdown') === 0) {
+      powerMonitor.unblockShutdown()
+    }
+  })
+}
 
 module.exports = powerMonitor