Periodically wake the WebSocket, when GCM is disabled

Use the WebSocketAlarm, to periodically wake the WebSocket and with
it, any threads that may be stuck in blocking wait, while the device
is sleeping.

Fixes signalapp#6644
// FREEBIE

src/org/thoughtcrime/securesms/service/MessageRetrievalService.java

@@ -20,6 +20,7 @@
 import org.whispersystems.libsignal.InvalidVersionException;
 import org.whispersystems.signalservice.api.SignalServiceMessagePipe;
 import org.whispersystems.signalservice.api.SignalServiceMessageReceiver;
+import org.whispersystems.signalservice.api.WebSocketAlarm;
 
 import java.util.LinkedList;
 import java.util.List;
@@ -50,6 +51,7 @@ public class MessageRetrievalService extends Service implements InjectableType,
   private int                    activeActivities = 0;
   private List<Intent>           pushPending      = new LinkedList<>();
   private MessageRetrievalThread retrievalThread  = null;
+  private WebSocketAlarm         webSocketAlarm   = null;
 
   public static SignalServiceMessagePipe pipe = null;
 
@@ -66,6 +68,10 @@ public void onCreate() {
     retrievalThread = new MessageRetrievalThread();
     retrievalThread.start();
 
+    if (TextSecurePreferences.isGcmDisabled(this)) {
+      webSocketAlarm = new WebSocketAlarm(this);
+    }
+
     setForegroundIfNecessary();
   }
 
@@ -87,6 +93,10 @@ public void onDestroy() {
       retrievalThread.stopThread();
     }
 
+    if (webSocketAlarm != null) {
+      webSocketAlarm.disable();
+    }
+
     sendBroadcast(new Intent("org.thoughtcrime.securesms.RESTART"));
   }