Add unit tests for the Background Scheduler.

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.ContextUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
+import org.chromium.chrome.browser.offlinepages.interfaces.SchedulerBridge;
 
 /**
  * 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 onProcessingDone(boolean result);
-    }
-
     // Starts processing of one or more queued background requests.
     // Returns whether processing was started and that caller should
     // expect a callback (once processing has completed or terminated).
     // If processing was already active or not able to process for
     // some other reason, returns false and this calling instance will
     // not receive a callback.
     // TODO(dougarnett): consider adding policy check api to let caller
     //     separately determine if not allowed by policy.
-    public static boolean startProcessing(ProcessingDoneCallback callback) {
+    public static boolean startProcessing(
+            SchedulerBridge.ProcessingDoneCallback callback) {
         return nativeStartProcessing(callback);
     }
 
     @CalledByNative
     private static void schedule() {
         BackgroundScheduler.schedule(ContextUtils.getApplicationContext());
     }
 
     @CalledByNative
     private static void unschedule() {
         BackgroundScheduler.unschedule(ContextUtils.getApplicationContext());
     }
 
-    private static native boolean nativeStartProcessing(ProcessingDoneCallback callback);
+    /**
+     * This interface defines the JNI callback available to native code. It must exactly match the
+     * {@link SchedulerBridge.ProcessingDoneCallback} interface (which is not tied to JNI and may be
+     * use for unit testing).  Due to JNI restrictions, the interface for this callback must be
+     * declared in the same java file, so there is only one XXX_jni.h file to include on the C++
+     * side (Otherwise, we get the JNI function RegisterNativesImpl multiply defined, and can't
+     * compile). This interface is exactly the same as the one in SchedulerBridge, and we're using
+     * duck typing to make sure the callback can work.
+     */
+    public interface ProcessingDoneCallback {
+        @CalledByNative("ProcessingDoneCallback")
+        void onProcessingDone(boolean result);
+    }
+
+    private static native boolean nativeStartProcessing(
+            SchedulerBridge.ProcessingDoneCallback callback);
 }