Add a heartbeat method that pings the server at a timed interval. Does

this using the newly added ping call without the use of bolts'
callbacks.
Implemented a TaskService class that is used to do the work offloaded
by the GcmNetworkManager which is used here to schedule
keep-alive recurring tasks.

app/src/main/AndroidManifest.xml

@@ -69,5 +69,13 @@
                 <action android:name="com.google.android.gms.iid.InstanceID"/>
             </intent-filter>
         </service>
+
+        <service android:name=".service.TaskService"
+            android:permission="com.google.android.gms.permission.BIND_NETWORK_TASK_SERVICE"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="com.google.android.gms.gcm.ACTION_TASK_READY"/>
+            </intent-filter>
+        </service>
     </application>
 </manifest>
\ No newline at end of file

app/src/main/java/chat/rocket/android/service/TaskService.java

+package chat.rocket.android.service;
+
+import com.google.android.gms.gcm.GcmNetworkManager;
+import com.google.android.gms.gcm.GcmTaskService;
+import com.google.android.gms.gcm.TaskParams;
+
+public class TaskService extends GcmTaskService {
+
+    public static final String TAG_KEEP_ALIVE = "TAG_KEEP_ALIVE";
+
+    @Override
+    public int onRunTask(TaskParams taskParams) {
+        switch (taskParams.getTag()) {
+            case TAG_KEEP_ALIVE:
+                ConnectivityManager.getInstance(getApplicationContext()).keepAliveServer();
+                return GcmNetworkManager.RESULT_SUCCESS;
+            default:
+                return GcmNetworkManager.RESULT_FAILURE;
+        }
+    }
+}