[sessions] Properly namespace recently-componentized TabRestore code

components/sessions/content/content_tab_client_data.h

 // 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.
 
 #ifndef COMPONENTS_SESSIONS_CONTENT_CONTENT_CLIENT_DATA_H_
 #define COMPONENTS_SESSIONS_CONTENT_CONTENT_CLIENT_DATA_H_
 
 #include "base/memory/ref_counted.h"
 #include "components/sessions/core/tab_restore_service_client.h"
 #include "components/sessions/sessions_export.h"
 #include "content/public/browser/session_storage_namespace.h"
 
+namespace content {
+class WebContents;
+}
+
 namespace sessions {
 
 // A //content-specific subclass of TabClientData that is used to associate
 // TabRestoreService::Tab instances with the content::SessionStorageNamespace
 // of the WebContents from which they were created.
 class SESSIONS_EXPORT ContentTabClientData : public TabClientData {
  public:
   explicit ContentTabClientData(content::WebContents* web_contents);
   ContentTabClientData();
   ~ContentTabClientData() override;
 
   content::SessionStorageNamespace* session_storage_namespace() const {
     return session_storage_namespace_.get();
   }
 
  private:
   // TabClientData:
   scoped_ptr<TabClientData> Clone() override;
 
   scoped_refptr<content::SessionStorageNamespace> session_storage_namespace_;
 };
 
 }  // namespace sessions
 
 #endif  // COMPONENTS_SESSIONS_CONTENT_CONTENT_CLIENT_DATA_H_