Set site engagement timestamps to privacy-respectful values when history is cleared.

components/history/core/browser/history_backend.cc

 // Copyright (c) 2012 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/history/core/browser/history_backend.h"
 
 #include <algorithm>
 #include <functional>
 #include <list>
 #include <map>
@@ skipping 406 matching lines @@
 
   auto top_hosts = db_->TopHosts(num_hosts);
 
   host_ranks_.clear();
   int i = 0;
   for (const auto& host_count : top_hosts)
     host_ranks_[host_count.first] = i++;
   return top_hosts;
 }
 
-OriginCountMap HistoryBackend::GetCountsForOrigins(
+OriginCountAndLastVisitMap HistoryBackend::GetCountsAndLastVisitForOrigins(
     const std::set<GURL>& origins) const {
   if (!db_)
-    return OriginCountMap();
+    return OriginCountAndLastVisitMap();
 
   URLDatabase::URLEnumerator it;
   if (!db_->InitURLEnumeratorForEverything(&it))
-    return OriginCountMap();
+    return OriginCountAndLastVisitMap();
 
-  OriginCountMap origin_count_map;
+  OriginCountAndLastVisitMap origin_count_map;
   for (const GURL& origin : origins)
-    origin_count_map[origin] = 0;
+    origin_count_map[origin] = std::make_pair(0, base::Time());
 
   URLRow row;
   while (it.GetNextURL(&row)) {
     GURL origin = row.url().GetOrigin();
-    if (ContainsValue(origins, origin))
-      ++origin_count_map[origin];
+    auto iter = origin_count_map.find(origin);
+    if (iter != origin_count_map.end()) {
+      std::pair<int, base::Time>& value = iter->second;
+      ++(value.first);
+      if (value.second.is_null() || value.second < row.last_visit())
+        value.second = row.last_visit();
+    }
   }
 
   return origin_count_map;
 }
 
 int HistoryBackend::HostRankIfAvailable(const GURL& url) const {
   auto it = host_ranks_.find(HostForTopHosts(url));
   return it != host_ranks_.end() ? it->second : kMaxTopHosts;
 }
 
@@ skipping 2167 matching lines @@
   // transaction is currently open.
   db_->CommitTransaction();
   db_->Vacuum();
   db_->BeginTransaction();
   db_->GetStartDate(&first_recorded_time_);
 
   return true;
 }
 
 }  // namespace history