Add restart helper on Windows

src/browser/auto-updater-win32.coffee

@@ -1,6 +1,5 @@
 {EventEmitter} = require 'events'
 _ = require 'underscore-plus'
-shellAutoUpdater = require 'auto-updater'
 SquirrelUpdate = require './squirrel-update'
 
 class AutoUpdater
@@ -12,11 +11,9 @@ class AutoUpdater
     console.log 'restarting new atom.exe'
 
     if SquirrelUpdate.existsSync()
-      SquirrelUpdate.spawn ['--processStart', 'atom.exe'], ->
-        console.log 'spawned new atom.exe'
-        shellAutoUpdater.quitAndInstall()
+      SquirrelUpdate.restartAtom()
     else
-      shellAutoUpdater.quitAndInstall()
+      require('auto-updater').quitAndInstall()
 
   downloadUpdate: (callback) ->
     SquirrelUpdate.spawn ['--download', @updateUrl], (error, stdout) ->

src/browser/squirrel-update.coffee

@@ -36,7 +36,7 @@ spawn = (command, args, callback) ->
     error ?= new Error("Command failed: #{signal ? code}") if code isnt 0
     error?.code ?= code
     error?.stdout ?= stdout
-    callback(error, stdout)
+    callback?(error, stdout)
 
 # Spawn reg.exe and callback when it completes
 spawnReg = (args, callback) ->
@@ -175,6 +175,11 @@ exports.spawn = spawnUpdate
 exports.existsSync = ->
   fs.existsSync(updateDotExe)
 
+# Restart Atom using the version pointed to by the atom.cmd shim
+exports.restartAtom = ->
+  app.once 'will-quit', -> spawn(path.join(binFolder, 'atom.cmd'))
+  app.quit()
+
 # Handle squirrel events denoted by --squirrel-* command line arguments.
 exports.handleStartupEvent = ->
   switch process.argv[1]