[Sync] Creating sync_sessions component, moving revisit logic.

components/sync_sessions/revisit/page_visit_observer.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_SYNC_DRIVER_REVISIT_PAGE_VISIT_OBSERVERE_H_
-#define COMPONENTS_SYNC_DRIVER_REVISIT_PAGE_VISIT_OBSERVERE_H_
+#ifndef COMPONENTS_SYNC_SESSIONS_REVISIT_PAGE_VISIT_OBSERVER_H_
+#define COMPONENTS_SYNC_SESSIONS_REVISIT_PAGE_VISIT_OBSERVER_H_
 
-#include "url/gurl.h"
+#include <string>
 
-namespace sync_driver {
+#include "base/time/time.h"
+
+class GURL;
+
+namespace sync_sessions {
 
 // An interface that allows observers to be notified when a page is visited.
 class PageVisitObserver {
  public:
   // This enum represents the most common ways to visit a new page/URL.
   enum TransitionType {
     kTransitionPage = 0,
     kTransitionOmniboxUrl = 1,
     kTransitionOmniboxDefaultSearch = 2,
     kTransitionOmniboxTemplateSearch = 3,
     kTransitionBookmark = 4,
     kTransitionCopyPaste = 5,
     kTransitionForwardBackward = 6,
     kTransitionRestore = 7,
     kTransitionUnknown = 8,
     kTransitionTypeLast = 9,
   };
 
   virtual ~PageVisitObserver() {}
   virtual void OnPageVisit(const GURL& url,
                            const TransitionType transition) = 0;
 };
 
-}  // namespace sync_driver
+}  // namespace sync_sessions
 
-#endif  // COMPONENTS_SYNC_DRIVER_REVISIT_PAGE_VISIT_OBSERVERE_H_
+#endif  // COMPONENTS_SYNC_SESSIONS_REVISIT_PAGE_VISIT_OBSERVER_H_