key to fetch response of chrome push notification at android side

#i am using chrome push notification word press plugin. it send notification at background side at android but i don't know the key to fetch response at android side.i had already "notification" "notifications" "data"..but don't work. please help me.

public function sendGCM($data) {

    $this->putNotificationOnQueue($data);

    $apiKey = get_option('web_push_api_key');
    $url = 'http://ift.tt/YbbTRA';
    $id = $this->getClientIds();

    if (empty($id)) {
        return 'No subscribers on your site yet!';
    }

    if (count($id) >= 1000) {
        $newId = array_chunk($id, 1000);
        foreach ($newId as $inner_id) {
            $fields = array(
                'registration_ids' => $inner_id,
            );
            $headers = array(
                'Authorization: key=' . $apiKey,
                'Content-Type: application/json');

            $ch = curl_init();
            curl_setopt($ch, CURLOPT_URL, $url);
            curl_setopt($ch, CURLOPT_POST, true);
            curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
            curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
            $result = curl_exec($ch);
            //print_r($result);
        }
    } else {
        $fields = array(
            'registration_ids' => $id,
        );
        $headers = array(
            'Authorization: key=' . $apiKey,
            'Content-Type: application/json');

        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
        $result = curl_exec($ch);
    }

    $answer = json_decode($result);
    curl_close($ch);

    if ($answer) {
        $this->cleanClientIds($answer);
    }

    return $result;
}

via Chebli Mohamed