function disableMarkedExtensions() {
        return Async.doInParallel_aggregateErrors(
            Object.keys(_idsToDisable),
            function (id) {
                return disable(id);
            }
        );
    }
Disables extensions marked for disabling.

If the return promise is rejected, the argument will contain an array of objects. Each
element is an object identifying the extension failed with "item" property set to the
extension id which has failed to be disabled and "error" property set to the error.

@return {$.Promise} A promise that's resolved when all extensions marked for disabling are
     disabled or rejected if one or more extensions can't be disabled.