feat($http): add notify callback

Allows progress notifications for $http requests.

This makes use of the readyState 3 of XMLHttpRequest.

Author: chrisirhc

src/ng/http.js

@@ -905,7 +905,7 @@ function $HttpProvider() {
       // if we won't have the response in cache, send the request to the backend
       if (!cachedResp) {
         $httpBackend(config.method, url, reqData, done, reqHeaders, config.timeout,
-            config.withCredentials, config.responseType);
+            config.withCredentials, config.responseType, notify);
       }
 
       return promise;
@@ -932,6 +932,14 @@ function $HttpProvider() {
       }
 
 
+      /**
+       * Notify callback registered to $httpBackend()
+       */
+      function notify(xhr) {
+        deferred.notify(xhr);
+      }
+
+
       /**
        * Resolves the raw $http promise.
        */

src/ng/httpBackend.js

@@ -32,7 +32,7 @@ function $HttpBackendProvider() {
 
 function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument, locationProtocol) {
   // TODO(vojta): fix the signature
-  return function(method, url, post, callback, headers, timeout, withCredentials, responseType) {
+  return function(method, url, post, callback, headers, timeout, withCredentials, responseType, notify) {
     var status;
     $browser.$$incOutstandingRequestCount();
     url = url || $browser.url();
@@ -92,6 +92,8 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument,
               status || xhr.status,
               (xhr.responseType ? xhr.response : xhr.responseText),
               responseHeaders);
+        } else if (xhr && xhr.readyState == 3 && notify) {
+          notify(xhr);
         }
       };