[Sync] Creating sync_sessions component, moving revisit logic.

components/sync_sessions/revisit/offset_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_OFFSET_TAB_MATCHER_H_
-#define COMPONENTS_SYNC_DRIVER_OFFSET_TAB_MATCHER_H_
+#ifndef COMPONENTS_SYNC_SESSIONS_REVISIT_OFFSET_TAB_MATCHER_H_
+#define COMPONENTS_SYNC_SESSIONS_REVISIT_OFFSET_TAB_MATCHER_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"
+#include "components/sync_sessions/revisit/page_equality.h"
+#include "components/sync_sessions/revisit/page_visit_observer.h"
 
-namespace sync_driver {
+namespace sync_sessions {
 
 // This class looks for tabs that have matching pages that are not the current
 // navigation entry. This corresponds to the pages you would arrive at if you
 // pressed the forward/backwards buttons. The goal is to emit metrics for the
 // most recent/current entry. So to break ties of multiple entries that match,
 // first the timestamp on the tab is used, followed by the index of the entry.
 // This isn't necessarily perfect at determining the most recent, but it should
 // be a reasonable enough approximation.
 class OffsetTabMatcher {
  public:
   explicit OffsetTabMatcher(const PageEquality& page_equality);
   void Check(const sessions::SessionTab* tab);
   void Emit(const PageVisitObserver::TransitionType transition);
 
  private:
   int Clamp(int input, int lower, int upper);
 
   const PageEquality page_equality_;
   const sessions::SessionTab* best_tab_ = nullptr;
   // Invalid while best_tab_ is nullptr.
   int best_offset_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(OffsetTabMatcher);
 };
 
-}  // namespace sync_driver
+}  // namespace sync_sessions
 
-#endif  // COMPONENTS_SYNC_DRIVER_OFFSET_TAB_MATCHER_H_
+#endif  // COMPONENTS_SYNC_SESSIONS_REVISIT_OFFSET_TAB_MATCHER_H_