feat(clearCache): clearCache returns a promise

Closes #3724

Author: abcd-ca

Diff for: js/angular/service/history.js

@@ -648,11 +648,12 @@ function($rootScope, $state, $location, $window, $timeout, $ionicViewSwitcher, $
     /**
      * @ngdoc method
      * @name $ionicHistory#clearCache
+	 * @return promise
      * @description Removes all cached views within every {@link ionic.directive:ionNavView}.
      * This both removes the view element from the DOM, and destroy it's scope.
      */
     clearCache: function(stateIds) {
-      $timeout(function() {
+      return $timeout(function() {
         $ionicNavViewDelegate._instances.forEach(function(instance) {
           instance.clearCache(stateIds);
         });