Abstract content::SessionStorageNamespace from core TabRestore code

components/sessions/core/tab_restore_service_client.cc

+// Copyright 2015 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 "components/sessions/core/tab_restore_service_client.h"
+
+namespace sessions {
+
+TabClientData::~TabClientData() {}
+
+TabRestoreServiceClient::~TabRestoreServiceClient() {}
+
+scoped_ptr<TabClientData>
+TabRestoreServiceClient::GetTabClientDataForWebContents(
+    content::WebContents* web_contents) {
+  return nullptr;
+}
+
+void TabRestoreServiceClient::OnTabRestored(const GURL& url) {}
+
+}  // namespace sessions