Enable harmony collections, also revert previous WeakMap hack.

Fixed atom/atom-shell#7.

src/main.coffee

@@ -13,10 +13,14 @@ class BrowserMain
   constructor: ->
     @windowState = {}
 
+    @setupJavaScriptArguments()
     @parseCommandLine()
     @setupNodePaths()
     @handleEvents()
 
+  setupJavaScriptArguments: ->
+    app.commandLine.appendSwitch 'js-flags', '--harmony_collections'
+
   parseCommandLine: ->
     modifiedArgv = ['node'].concat(process.argv) # optimist assumes the first arg will be node
     args = optimist(modifiedArgv).argv

src/stdlib/subscriber.coffee

@@ -1,14 +1,5 @@
 _ = require 'underscore'
 
-class WeakMap
-  constructor: ->
-    @map = {}
-
-  set: (key, value) -> @map[key] = value
-  get: (key) -> @map[key]
-  delete: (key) -> delete @map[key]
-  has: (key) -> @map[key]?
-
 module.exports =
   subscribe: (eventEmitter, eventName, callback) ->
     eventEmitter.on eventName, callback