Add hidden --socket-path flag

This will allow integration tests to control which atom application
instance they use when creating atom windows

src/browser/atom-application.coffee

@@ -14,7 +14,7 @@ url = require 'url'
 {EventEmitter} = require 'events'
 _ = require 'underscore-plus'
 
-socketPath =
+DEFAULT_SOCKET_PATH =
   if process.platform is 'win32'
     '\\\\.\\pipe\\atom-sock'
   else
@@ -31,17 +31,20 @@ class AtomApplication
 
   # Public: The entry point into the Atom application.
   @open: (options) ->
+    options.socketPath ?= DEFAULT_SOCKET_PATH
+
     createAtomApplication = -> new AtomApplication(options)
 
     # FIXME: Sometimes when socketPath doesn't exist, net.connect would strangely
     # take a few seconds to trigger 'error' event, it could be a bug of node
     # or atom-shell, before it's fixed we check the existence of socketPath to
     # speedup startup.
-    if (process.platform isnt 'win32' and not fs.existsSync socketPath) or options.test
+    if (process.platform isnt 'win32' and not fs.existsSync options.socketPath) or options.test
       createAtomApplication()
       return
 
-    client = net.connect {path: socketPath}, ->
+
+    client = net.connect {path: options.socketPath}, ->
       client.write JSON.stringify(options), ->
         client.end()
         app.terminate()
@@ -57,7 +60,7 @@ class AtomApplication
   exit: (status) -> app.exit(status)
 
   constructor: (options) ->
-    {@resourcePath, @version, @devMode, @safeMode} = options
+    {@resourcePath, @version, @devMode, @safeMode, @socketPath} = options
 
     # Normalize to make sure drive letter case is consistent on Windows
     @resourcePath = path.normalize(@resourcePath) if @resourcePath
@@ -119,15 +122,15 @@ class AtomApplication
       connection.on 'data', (data) =>
         @openWithOptions(JSON.parse(data))
 
-    server.listen socketPath
+    server.listen @socketPath
     server.on 'error', (error) -> console.error 'Application server failed', error
 
   deleteSocketFile: ->
     return if process.platform is 'win32'
 
-    if fs.existsSync(socketPath)
+    if fs.existsSync(@socketPath)
       try
-        fs.unlinkSync(socketPath)
+        fs.unlinkSync(@socketPath)
       catch error
         # Ignore ENOENT errors in case the file was deleted between the exists
         # check and the call to unlink sync. This occurred occasionally on CI

src/browser/main.coffee

@@ -120,6 +120,7 @@ parseCommandLine = ->
   options.alias('t', 'test').boolean('t').describe('t', 'Run the specified specs and exit with error code on failures.')
   options.alias('v', 'version').boolean('v').describe('v', 'Print the version.')
   options.alias('w', 'wait').boolean('w').describe('w', 'Wait for window to be closed before returning.')
+  options.string('socket-path')
   args = options.argv
 
   if args.help
@@ -140,6 +141,7 @@ parseCommandLine = ->
   newWindow = args['new-window']
   pidToKillWhenClosed = args['pid'] if args['wait']
   logFile = args['log-file']
+  socketPath = args['socket-path']
 
   if args['resource-path']
     devMode = true
@@ -164,6 +166,6 @@ parseCommandLine = ->
   # explicitly pass it by command line, see http://git.io/YC8_Ew.
   process.env.PATH = args['path-environment'] if args['path-environment']
 
-  {resourcePath, pathsToOpen, executedFrom, test, version, pidToKillWhenClosed, devMode, safeMode, newWindow, specDirectory, logFile}
+  {resourcePath, pathsToOpen, executedFrom, test, version, pidToKillWhenClosed, devMode, safeMode, newWindow, specDirectory, logFile, socketPath}
 
 start()