[Closure Externs] Handle optional params sent to an API callback

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 45 matching lines @@
     object dict;
 
     static void go();
     static void stop();
   };
 
   callback VoidCallback = void();
 
   callback BazGreekCallback = void(Baz baz, Greek greek);
 
+  callback OptionalParamCallback = void(optional Qux qux);
+
   interface Functions {
     // Does something exciting! And what's more, this is a multiline function
     // comment! It goes onto multiple lines!
     // |baz| : The baz to use.
     static void doSomething(Baz baz, VoidCallback callback);
 
     // |callback| : The callback which will most assuredly in all cases be
     // called; that is, of course, iff such a callback was provided and is
     // not at all null.
     static void bazGreek(optional BazGreekCallback callback);
 
     [deprecated="Use a new method."] static DOMString returnString();
+
+    static void optionalParam(optional OptionalParamCallback callback);
   };
 
   interface Events {
     // Fired when we realize it's a trap!
     static void onTrapDetected(Baz baz);
   };
 };
 """
 
 # The output we expect from our fake idl file.
@@ skipping 110 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
+ * @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]))
 
 
 fake_json = """// Copyright 2014 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.
@@ skipping 137 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()