[Sync] Creating sync_sessions component, moving revisit logic.

components/sync_driver/revisit/current_tab_matcher.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/sync_driver/revisit/current_tab_matcher.h"
-
-#include "base/metrics/histogram_macros.h"
-#include "base/time/time.h"
-#include "components/sessions/core/serialized_navigation_entry.h"
-
-namespace sync_driver {
-
-CurrentTabMatcher::CurrentTabMatcher(const PageEquality& page_equality)
-    : page_equality_(page_equality) {}
-
-void CurrentTabMatcher::Check(const sessions::SessionTab* tab) {
-  if (tab->navigations.empty()) {
-    return;
-  }
-  const sessions::SerializedNavigationEntry& currentEntry =
-      tab->navigations[tab->normalized_navigation_index()];
-  // Cannot rely on SerializedNavigationEntry timestamps, they're
-  // not set for foreign sessions. Instead rely on tab timestamps.
-  if (page_equality_.IsSamePage(currentEntry.virtual_url()) &&
-      (most_recent_match_ == nullptr ||
-       tab->timestamp > most_recent_match_->timestamp)) {
-    most_recent_match_ = tab;
-  }
-}
-
-void CurrentTabMatcher::Emit(
-    const PageVisitObserver::TransitionType transition) {
-  if (most_recent_match_ == nullptr) {
-    UMA_HISTOGRAM_ENUMERATION("Sync.PageRevisitTabMissTransition", transition,
-                              PageVisitObserver::kTransitionTypeLast);
-  } else {
-    base::TimeDelta age(base::Time::Now() - most_recent_match_->timestamp);
-    UMA_HISTOGRAM_CUSTOM_TIMES("Sync.PageRevisitTabMatchAge", age,
-                               base::TimeDelta::FromSeconds(1),
-                               base::TimeDelta::FromDays(14), 100);
-    UMA_HISTOGRAM_ENUMERATION("Sync.PageRevisitTabMatchTransition", transition,
-                              PageVisitObserver::kTransitionTypeLast);
-  }
-}
-
-}  // namespace sync_driver