[Android] BackgroundTaskScheduler reschedule implementation

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 79705bf0da5f347ec67c7cccc08b0b9acc1f97e8..971bebbd5e0576de4f7d72fb8c0745380d30bc50 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
@@ -8,6 +8,7 @@ import android.annotation.TargetApi;
 import android.os.Build;
 
 import org.chromium.base.ThreadUtils;
+import org.chromium.base.VisibleForTesting;
 
 /**
  * A factory for {@link BackgroundTaskScheduler} that ensures there is only ever a single instance.
@@ -34,6 +35,11 @@ public final class BackgroundTaskSchedulerFactory {
         return sInstance;
     }
 
+    @VisibleForTesting
+    static void setSchedulerForTesting(BackgroundTaskScheduler scheduler) {
+        sInstance = scheduler;
+    }
+
     // Do not instantiate.
     private BackgroundTaskSchedulerFactory() {}
 }