[Sync] Creating sync_sessions component, moving revisit logic.

components/sync_driver/revisit/current_tab_matcher.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_CURRENT_TAB_MATCHER_H_
-#define COMPONENTS_SYNC_DRIVER_CURRENT_TAB_MATCHER_H_
-
-#include "base/gtest_prod_util.h"
-#include "components/sessions/core/session_types.h"
-#include "components/sync_driver/revisit/page_equality.h"
-#include "components/sync_driver/revisit/page_visit_observer.h"
-
-namespace sync_driver {
-
-// This class checks the current navigation entry for the given tabs to see if
-// they correspond to the same page we were constructed to look for. Upon
-// finding multiple matches, the most recently modified will be chosen.
-class CurrentTabMatcher {
- public:
-  explicit CurrentTabMatcher(const PageEquality& page_equality);
-  void Check(const sessions::SessionTab* tab);
-  void Emit(const PageVisitObserver::TransitionType transition);
-
- private:
-  FRIEND_TEST_ALL_PREFIXES(CurrentTabMatcherTest, Timestamp);
-
-  const PageEquality page_equality_;
-  const sessions::SessionTab* most_recent_match_ = nullptr;
-
-  DISALLOW_COPY_AND_ASSIGN(CurrentTabMatcher);
-};
-
-}  // namespace sync_driver
-
-#endif  // COMPONENTS_SYNC_DRIVER_CURRENT_TAB_MATCHER_H_