Converted RegistrationIntentService to a JobIntentService (#436)

* Converted RegistrationIntentService to a JobIntentService

There appears to be a hard-to-reproduce hang that in the
RegistrationIntentService, which is probably related to it being an
IntentService instead of a JobIntentService.

Author: Alex Ames

messaging/AndroidManifest.xml

@@ -22,6 +22,7 @@
     </service>
 
     <service android:name="com.google.firebase.messaging.cpp.RegistrationIntentService"
+             android:permission="android.permission.BIND_JOB_SERVICE"
              android:exported="false" >
     </service>
   </application>

messaging/src/android/java/com/google/firebase/messaging/JobIds.java

@@ -20,4 +20,5 @@ public final class JobIds {
   private JobIds() {}
 
   public static final int MESSAGE_FORWARDING_SERVICE = 1000;
+  public static final int REGISTRATION_INTENT_SERVICE = 1001;
 }

messaging/src/android/java/com/google/firebase/messaging/cpp/RegistrationIntentService.java

@@ -14,9 +14,9 @@
 
 package com.google.firebase.messaging.cpp;
 
-import android.app.IntentService;
 import android.content.Context;
 import android.content.Intent;
+import androidx.core.app.JobIntentService;
 import com.google.firebase.iid.FirebaseInstanceId;
 import com.google.flatbuffers.FlatBufferBuilder;
 import java.io.FileOutputStream;
@@ -28,20 +28,14 @@
  * A class that manages Registration Token generation and passes the generated tokens to the native
  * OnTokenReceived function.
  */
-public class RegistrationIntentService extends IntentService {
+public class RegistrationIntentService extends JobIntentService {
   private static final String TAG = "FirebaseRegService";
 
-  public RegistrationIntentService() {
-    // The tag here is used only to name the worker thread; it's important only for debugging.
-    // http://developer.android.com/reference/android/app/IntentService.html#IntentService(java.lang.String)
-    super(TAG);
-  }
-
   // Fetch the latest registration token and notify the C++ layer.
   @Override
-  protected void onHandleIntent(Intent intent) {
+  protected void onHandleWork(Intent intent) {
     String token = FirebaseInstanceId.getInstance().getToken();
-    DebugLogging.log(TAG, String.format("onHandleIntent token=%s", token));
+    DebugLogging.log(TAG, String.format("onHandleWork token=%s", token));
     if (token != null) {
       writeTokenToInternalStorage(this, token);
     }