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

components/history/core/browser/history_backend.cc

Index: components/history/core/browser/history_backend.cc
diff --git a/components/history/core/browser/history_backend.cc b/components/history/core/browser/history_backend.cc
index 9cee47e892206bc47375990ca108894dcadbdcfa..eb4dae22d2f7e3e4321fc9e62a52c334393d0a6a 100644
--- a/components/history/core/browser/history_backend.cc
+++ b/components/history/core/browser/history_backend.cc
@@ -424,7 +424,7 @@ TopHostsList HistoryBackend::TopHosts(size_t num_hosts) const {
   return top_hosts;
 }
 
-OriginCountMap HistoryBackend::GetCountsForOrigins(
+OriginCountMap HistoryBackend::GetCountsAndLastVisitForOrigins(
     const std::set<GURL>& origins) const {
   if (!db_)
     return OriginCountMap();
@@ -435,13 +435,17 @@ OriginCountMap HistoryBackend::GetCountsForOrigins(
 
   OriginCountMap 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];
+    if (ContainsValue(origins, origin)) {

[sdefresne, 2016/04/19 07:18:01]

nit: I would change to this instead to avoid doing two lookups in the map:

auto iter = origins.find(origin);
if (iter != origins.end()) {
  std::pair<int, base::Time>& value = *iter;
  ...
}

[dominickn, 2016/04/19 07:59:32]

Done.

+      std::pair<int, base::Time>& value = origin_count_map[origin];
+      ++(value.first);
+      if (value.second.is_null() || value.second < row.last_visit())
+        value.second = row.last_visit();
+    }
   }
 
   return origin_count_map;