Add error event to atom global

src/atom.coffee

@@ -127,6 +127,10 @@ class Atom extends Model
   # (both spec and application). Call after this instance has been assigned to
   # the `atom` global.
   initialize: ->
+    window.onerror = =>
+      @openDevTools()
+      @emit 'error', arguments
+
     @unsubscribe()
     @setBodyPlatformClass()
 

src/window.coffee

@@ -1,6 +1,3 @@
-window.onerror = ->
-  atom.openDevTools()
-
 # Public: Measure how long a function takes to run.
 #
 # * description: