Emit process exit event with app exit code

atom/browser/api/lib/app.coffee

@@ -34,6 +34,18 @@ app.setAppPath = (path) ->
 app.getAppPath = ->
   appPath
 
+appExitCode = undefined
+app.exit = (exitCode) ->
+  appExitCode = exitCode
+  app._exit(exitCode)
+
+# Map process.exit to app.exit, which quits gracefully.
+process.exit = app.exit
+
+# Emit a process 'exit' event on app quit.
+app.on 'quit', ->
+  process.emit 'exit', appExitCode
+
 # Routes the events to webContents.
 for name in ['login', 'certificate-error', 'select-client-certificate']
   do (name) ->