Add dialog API.

Supported APIs:
* openFile
* openMultiFiles
* openFolder
* saveAs

Each API is asynchronous and accepts a callback.

browser/api/lib/dialog.coffee

@@ -0,0 +1,51 @@
+EventEmitter = require('events').EventEmitter
+ipc = require 'ipc'
+
+FileDialog = process.atomBinding('file_dialog').FileDialog
+FileDialog.prototype.__proto__ = EventEmitter.prototype
+
+callbacksInfo = {}
+
+fileDialog = new FileDialog
+
+onSelected = (event, id, paths...) ->
+  {processId, routingId} = callbacksInfo[id]
+  delete callbacksInfo[id]
+
+  ipc.sendChannel processId, routingId, 'ATOM_RENDERER_DIALOG', id, paths...
+
+fileDialog.on 'selected', onSelected
+fileDialog.on 'cancelled', onSelected
+
+validateOptions = (options) ->
+  return false unless typeof options is 'object'
+
+  options.fileTypes = [] unless Array.isArray options.fileTypes
+  for type in options.fileTypes
+    return false unless typeof type is 'object' and
+                        typeof type.description is 'string'
+                        Array.isArray type.extensions
+
+  options.defaultPath = '' unless options.defaultPath?
+  options.fileTypeIndex = 0 unless options.fileTypeIndex?
+  options.defaultExtension = '' unless options.defaultExtension?
+
+  true
+
+ipc.on 'ATOM_BROWSER_FILE_DIALOG', (processId, routingId, callbackId, type, title, options) ->
+  options = {} unless options?
+  options.type = type
+  options.title = title unless options.title?
+
+  throw new TypeError('Bad arguments') unless validateOptions options
+
+  callbacksInfo[callbackId] = processId: processId, routingId: routingId
+
+  fileDialog.selectFile processId, routingId,
+                        options.type,
+                        options.title,
+                        options.defaultPath,
+                        options.fileTypes,
+                        options.fileTypeIndex,
+                        options.defaultExtension,
+                        callbackId