Adds initial JNI bridge code for Background Scheduler implementation.

chrome/android/java/src/org/chromium/chrome/browser/offlinepages/BackgroundSchedulerBridge.java

+// Copyright 2016 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.chrome.browser.offlinepages;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.chrome.browser.profiles.Profile;
+
+/**
+ * Provides Java scheduling support from native offlining code as
+ * well as JNI interface to tell native code to start processing
+ * queued requests.
+ */
+@JNINamespace("offline_pages::android")
+public class BackgroundSchedulerBridge {
+
+    /**
+     * Callback used to determine when request processing is done.
+     */
+    public interface ProcessingDoneCallback {
+        @CalledByNative("ProcessingDoneCallback")
+        void onResult();

[fgorski, 2016/04/28 11:44:00]

Do we not want to pass anything for result? Even if that would mean passing a
boolean. (e.g. no more tasks left vs. still some work to do)

Also, as Justin pointed out to me yesterday, please check out
org.chromium.base.Callback

[dougarnett, 2016/04/28 22:45:23]

I think we will want to return boolean - possible use is return code to
GcmTaskService, UMA, and testing. Talked with Justin, might not be able
to use that Callback for CalledByNative

+    }
+
+    public static boolean startProcessing(

[fgorski, 2016/04/28 11:44:00]

documentation.

[dougarnett, 2016/04/28 22:45:23]

Done.

+            Profile profile, ProcessingDoneCallback callback) {
+        return nativeStartProcessing(profile, callback);
+    }
+
+    @CalledByNative
+    private static void ensureScheduled() {

[fgorski, 2016/04/28 11:44:00]

schedule/unschedule.

After all the semantics of being scheduled multiple times versus only once can
be hidden from all other classes. WDYT?

[dougarnett, 2016/04/28 22:45:23]

As discussed, do like that better along with adding comments about their
separate idempotency.

+        // TODO(dougarnett): call GcmNetworkManager to schedule for
+        //     OfflinePageUtils.TASK_TAG.
+    }
+
+    @CalledByNative
+    private static void clearScheduled() {
+        // TODO(dougarnett): call GcmNetworkManager to unschedule for
+        //     OfflinePageUtils.TASK_TAG.
+    }
+
+    private static native boolean nativeStartProcessing(
+            Profile profile, ProcessingDoneCallback callback);
+}
+