Add skeleton code to wire Local- and Remote- file sync services

chrome/browser/sync_file_system/change_observer_interface.h

+// Copyright (c) 2012 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.
+
+#ifndef CHROME_BROWSER_SYNC_FILE_SYSTEM_CHANGE_OBSERVER_INTERFACE_H_
+#define CHROME_BROWSER_SYNC_FILE_SYSTEM_CHANGE_OBSERVER_INTERFACE_H_
+
+#include "base/basictypes.h"
+
+namespace sync_file_system {
+
+class LocalChangeObserver {
+ public:
+  LocalChangeObserver() {}
+  virtual ~LocalChangeObserver() {}
+
+  // This is called when there're one ore more local changes are available.
+  // |pending_changes_hint| indicates the pending queue length to help sync
+  // scheduling but the value may not be accurately reflect the real-time
+  // value.
+  virtual void OnLocalChangeAvailable(int64 pending_changes_hint) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LocalChangeObserver);
+};
+
+class RemoteChangeObserver {
+ public:
+  RemoteChangeObserver() {}
+  virtual ~RemoteChangeObserver() {}
+
+  // This is called when there're one ore more remote changes are available.
+  // |pending_changes_hint| indicates the pending queue length to help sync
+  // scheduling but the value may not be accurately reflect the real-time
+  // value.
+  virtual void OnRemoteChangeAvailable(int64 pending_changes_hint) = 0;
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RemoteChangeObserver);
+};
+
+}  // namespace sync_file_system
+
+#endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_CHANGE_OBSERVER_INTERFACE_H_