MD Settings: Add helper method for responding to cr.sendWithPromise.

ui/webui/resources/js/cr.js

 // Copyright (c) 2012 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.
 
 /**
  * The global object.
  * @type {!Object}
  * @const
  */
 var global = this;
@@ skipping 313 matching lines @@
   /**
    * The named method the WebUI handler calls directly in response to a
    * chrome.send call that expects a response. The handler requires no knowledge
    * of the specific name of this method, as the name is passed to the handler
    * as the first argument in the arguments list of chrome.send. The handler
    * must pass the ID, also sent via the chrome.send arguments list, as the
    * first argument of the JS invocation; additionally, the handler may
    * supply any number of other arguments that will be included in the response.
    * @param {string} id The unique ID identifying the Promise this response is
    *     tied to.
-   * @param {...*} var_args Variable number of arguments to be included in the
-   *     response.
+   * @param {*} response The response as sent from C++.
    */
-  function webUIResponse(id, var_args) {
+  function webUIResponse(id, response) {
     var resolverFn = chromeSendResolverMap[id];
     delete chromeSendResolverMap[id];
-    // Promise#resolve accepts only one value, therefore wrapping all arguments
-    // passed from C++ to JS in an array.
-    resolverFn(Array.prototype.slice.call(arguments, 1));

[Dan Beam, 2016/01/27 00:23:57]

why did you change this?

[dpapad, 2016/01/27 00:45:24]

Explained better in CL description. On top of that, if we were to support
variable number of args in CallJavascriptCallback helper, we would have to add
multiple signatures (similar to CallJavaScriptFunction at
https://code.google.com/p/chromium/codesearch#chromium/src/content/public/bro...),
I don't see a good reason to do this.

[Dan Beam, 2016/01/27 02:30:44]

I saw that
i understand that
I think the currently proposed mechanism will inspire lots of extra C++
base::ListValues to wrap things in, which is likely more verbose than this
0-line gain in JS.

we'll see!

+    resolverFn(response);
   }
 
   /**
    * A variation of chrome.send, suitable for messages that expect a single
    * response from C++.
    * @param {string} methodName The name of the WebUI handler API.
    * @param {...*} var_args Varibale number of arguments to be forwarded to the
    *     C++ call.
    * @return {!Promise}
    */
   function sendWithPromise(methodName, var_args) {
     var args = Array.prototype.slice.call(arguments, 1);
     return new Promise(function(resolve, reject) {
       var id = methodName + '_' + createUid();
       chromeSendResolverMap[id] = resolve;
-      chrome.send(methodName, ['cr.webUIResponse', id].concat(args));
+      chrome.send(methodName, [id].concat(args));
     });
   }
 
   /**
    * A registry of callbacks keyed by event name. Used by addWebUIListener to
    * register listeners.
    * @type {!Object<Array<Function>>}
    */
   var webUIListenerMap = Object.create(null);
 
@@ skipping 59 matching lines @@
     get isChromeOS() {
       return /CrOS/.test(navigator.userAgent);
     },
 
     /** Whether this is on vanilla Linux (not chromeOS). */
     get isLinux() {
       return /Linux/.test(navigator.userAgent);
     },
   };
 }();