[Android] Adding scheduling through GcmNetworkManager

components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java

Index: components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java
diff --git a/components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java b/components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java
index 239e855f777003e2a7f456f6bd502646bdd757b2..79705bf0da5f347ec67c7cccc08b0b9acc1f97e8 100644
--- a/components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java
+++ b/components/background_task_scheduler/android/java/src/org/chromium/components/background_task_scheduler/BackgroundTaskSchedulerFactory.java
@@ -20,7 +20,7 @@ public final class BackgroundTaskSchedulerFactory {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
             return new BackgroundTaskSchedulerJobService();
         } else {
-            throw new RuntimeException("Not able to schedule through GCM yet.");
+            return new BackgroundTaskSchedulerGcmNetworkManager();
         }
     }