[android] Add JobScheduler-based BackgroundTaskScheduler.

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

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.components.background_task_scheduler;
+
+import android.content.Context;
+
+/**
+ * The internal representation of a {@link BackgroundTaskScheduler} to make it possible to use
+ * system APIs ({@link android.app.job.JobScheduler} on newer platforms and GCM
+ * ({@link com.google.android.gms.gcm.GcmNetworkManager}) on older platforms.
+ */
+interface BackgroundTaskSchedulerDelegate {
+    /**
+     * Schedules a background task. See {@link TaskInfo} for information on what types of tasks that
+     * can be scheduled.
+     * @param context the current context.
+     * @param taskInfo the information about the task to be scheduled.
+     * @return true if the schedule operation succeeded, and false otherwise.
+     * @see TaskInfo
+     */
+    boolean schedule(Context context, TaskInfo taskInfo);
+
+    /**
+     * Cancels the task specified by the task ID.
+     * @param context the current context.
+     * @param taskId the ID of the task to cancel. See {@link TaskIds} for a list.
+     */
+    void cancel(Context context, int taskId);
+}