[Closure Externs] Add wrapping parens on optional params

tools/json_schema_compiler/js_externs_generator_test.py

 #!/usr/bin/env python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import idl_schema
 import json_parse
 from js_externs_generator import JsExternsGenerator
 from datetime import datetime
 import model
@@ skipping 191 matching lines @@
 chrome.fakeApi.bazGreek = function(callback) {};
 
 /**
  * @return {string}
  * @deprecated Use a new method.
  * @see https://developer.chrome.com/extensions/fakeApi#method-returnString
  */
 chrome.fakeApi.returnString = function() {};
 
 /**
- * @param {function(!chrome.fakeApi.Qux|undefined):void=} callback
+ * @param {function((!chrome.fakeApi.Qux|undefined)):void=} callback
  * @see https://developer.chrome.com/extensions/fakeApi#method-optionalParam
  */
 chrome.fakeApi.optionalParam = function(callback) {};
 
 /**
  * Fired when we realize it's a trap!
  * @type {!ChromeEvent}
  * @see https://developer.chrome.com/extensions/fakeApi#event-onTrapDetected
  */
 chrome.fakeApi.onTrapDetected;""" % (datetime.now().year, sys.argv[0]))
@@ skipping 142 matching lines @@
                               JsExternsGenerator().Generate(namespace).Render())
 
   def testJsonWithInlineObjects(self):
     namespace = self._GetNamespace(fake_json, 'fake_api.json', False)
     self.assertMultiLineEqual(json_expected,
                               JsExternsGenerator().Generate(namespace).Render())
 
 
 if __name__ == '__main__':
   unittest.main()