Add histograms and NetLog for host cache persistence

net/dns/host_cache.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 "net/dns/host_cache.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 324 matching lines @@
       auto addresses_value = base::MakeUnique<base::ListValue>();
       for (size_t i = 0; i < addresses.size(); ++i)
         addresses_value->AppendString(addresses[i].ToStringWithoutPort());
       entry_dict->SetList(kAddressesKey, std::move(addresses_value));
     }
 
     entry_list->Append(std::move(entry_dict));
   }
 }
 
-// TODO(mgersh): Add histograms to track failures.
 bool HostCache::RestoreFromListValue(const base::ListValue& old_cache) {
   for (auto it = old_cache.begin(); it != old_cache.end(); it++) {
     const base::DictionaryValue* entry_dict;
     if (!it->GetAsDictionary(&entry_dict))
       return false;
 
     std::string hostname;
     int address_family;
     HostResolverFlags flags;
     int error = OK;
@@ skipping 180 matching lines @@
     CACHE_HISTOGRAM_TIME("EraseValid.ValidFor", -stale.expired_by);
   }
 }
 
 void HostCache::RecordEraseAll(EraseReason reason, base::TimeTicks now) {
   for (const auto& it : entries_)
     RecordErase(reason, now, it.second);
 }
 
 }  // namespace net