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

ui/webui/resources/js/cr.js

Index: ui/webui/resources/js/cr.js
diff --git a/ui/webui/resources/js/cr.js b/ui/webui/resources/js/cr.js
index 984a5c25df05cf9cd2e9dafe5c79fe86c2843b6a..ddf7c87950035ee6e80710ee474a3b46aadfce2f 100644
--- a/ui/webui/resources/js/cr.js
+++ b/ui/webui/resources/js/cr.js
@@ -331,15 +331,12 @@ var cr = function() {
    * 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);
   }
 
   /**
@@ -355,7 +352,7 @@ var cr = function() {
     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));
     });
   }