[Sync] Refactor sync manager into interface.

sync/internal_api/public/sync_manager.cc

Index: sync/internal_api/public/sync_manager.cc
diff --git a/sync/internal_api/public/sync_manager.cc b/sync/internal_api/public/sync_manager.cc
new file mode 100644
index 0000000000000000000000000000000000000000..331a8af606777441bc0b4f347118acaaeebefd09
--- /dev/null
+++ b/sync/internal_api/public/sync_manager.cc
@@ -0,0 +1,19 @@
+// 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.
+
+#include "sync/internal_api/public/sync_manager.h"
+
+namespace syncer {
+
+SyncManager::ChangeDelegate::~ChangeDelegate() {}
+
+SyncManager::ChangeObserver::~ChangeObserver() {}
+
+SyncManager::Observer::~Observer() {}
+
+SyncManager::SyncManager() {}
+
+SyncManager::~SyncManager() {}
+
+}  // namespace syncer