WebUI: Replace cr.sendWithCallback with 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 a38c59f84732e820c00407287b3ef00c37b41bb2..2e62e975d2a7bc02ae853eb04aa969c33b3098e5 100644
--- a/ui/webui/resources/js/cr.js
+++ b/ui/webui/resources/js/cr.js
@@ -313,48 +313,52 @@ var cr = function() {
   }
 
   /**
-   * The mapping used by the sendWithCallback mechanism to tie the callback
-   * supplied to an invocation of sendWithCallback with the WebUI response
-   * sent by the browser in response to the chrome.send call. The mapping is
-   * from ID to callback function; the ID is generated by sendWithCallback and
-   * is unique across all invocations of said method.
-   * @type {!Object<Function>}
+   * The mapping used by the sendWithPromise mechanism to tie the Promise
+   * returned to callers with the corresponding WebUI response. The mapping is
+   * from ID to the Promise resolver function; the ID is generated by
+   * sendWithPromise and is unique across all invocations of said method.
+   * @type {!Map<string, !Function>}

[Dan Beam, 2016/01/23 02:48:51]

pretty sure this breaks safari, which is why jhawkins@ reverted it to Object<>
after also trying Map 6 month ago

https://codereview.chromium.org/1228183002

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Obje...

[dpapad, 2016/01/25 18:34:22]

Reverted.

I guess by "Safari" you mean Webkit-based browsers (chrome on IOS)? I would like
to understand a bit more about this, since I was planning to convert more places
in our JS code to use Map where possible, so questions.

 - What version of Safari/Webkit do we care about? According to
https://kangax.github.io/compat-table/es6/, IOS8/9 have most parts of Map
implemented already.
 - Are we missing the trybot that would catch this error?

    */
-  var chromeSendCallbackMap = Object.create(null);
+  var chromeSendResolverMap = new Map();
 
   /**
    * The named method the WebUI handler calls directly in response to a
-   * chrome.send call that expects a callback. The handler requires no knowledge
+   * 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 forwarded to the
-   * callback.
-   * @param {string} id The unique ID identifying the callback method this
-   *    response is tied to.
+   * 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.
    */
-  function webUIResponse(id) {
-    chromeSendCallbackMap[id].apply(
-        null, Array.prototype.slice.call(arguments, 1));
-    delete chromeSendCallbackMap[id];
+  function webUIResponse(id, var_args) {
+    var resolverFn = chromeSendResolverMap.get(id);
+    // If no response arguments where passed from C++, resolving the Promise
+    // without any arguments, else wraping all response arguments in an array
+    // since Promise#resolve accepts only one value.
+    var responseArgs = Array.prototype.slice.call(arguments, 1);
+    resolverFn(responseArgs.length == 0 ? undefined : responseArgs);
+    chromeSendResolverMap.delete(id);
   }
 
   /**
-   * A variation of chrome.send which allows the client to receive a direct
-   * callback without requiring the handler to have specific knowledge of any
-   * JS internal method names or state. The callback will be removed from the
-   * mapping once it has fired.
+   * 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 {Array|undefined} args Arguments for the method call sent to the
-   *     WebUI handler. Pass undefined if no args should be sent to the handler.
-   * @param {Function} callback A callback function which is called (indirectly)
-   *     by the WebUI handler.
+   * @param {...*} var_args Varibale number of arguments to be forwarded to the
+   *     C++ call.
+   * @return {!Promise}
    */
-  function sendWithCallback(methodName, args, callback) {
-    var id = methodName + createUid();
-    chromeSendCallbackMap[id] = callback;
-    chrome.send(methodName, ['cr.webUIResponse', id].concat(args || []));
+  function sendWithPromise(methodName, opt_args) {
+    var args = Array.prototype.slice.call(arguments, 1);
+    return new Promise(function(resolve, reject) {
+      var id = methodName + createUid();
+      chromeSendResolverMap.set(id, resolve);
+      chrome.send(methodName, ['cr.webUIResponse', id].concat(args));
+    });
   }
 
   /**
@@ -403,7 +407,7 @@ var cr = function() {
     getUid: getUid,
     makePublic: makePublic,
     webUIResponse: webUIResponse,
-    sendWithCallback: sendWithCallback,
+    sendWithPromise: sendWithPromise,
     webUIListenerCallback: webUIListenerCallback,
     addWebUIListener: addWebUIListener,
     PropertyKind: PropertyKind,