Add histograms and NetLog for host cache persistence

components/cronet/host_cache_persistence_manager.h

Index: components/cronet/host_cache_persistence_manager.h
diff --git a/components/cronet/host_cache_persistence_manager.h b/components/cronet/host_cache_persistence_manager.h
index 156f96639dc7679d1c0943076440b34105774983..2b160cfd2a5bc21b33d11e98854227c003d3106d 100644
--- a/components/cronet/host_cache_persistence_manager.h
+++ b/components/cronet/host_cache_persistence_manager.h
@@ -15,9 +15,14 @@
 #include "base/timer/timer.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "net/dns/host_cache.h"
+#include "net/log/net_log_with_source.h"
 
 class PrefService;
 
+namespace net {
+class NetLog;
+}
+
 namespace cronet {
 // Handles the interaction between HostCache and prefs for persistence.
 // When notified of a change in the HostCache, starts a timer, or ignores if the
@@ -40,7 +45,8 @@ class HostCachePersistenceManager : public net::HostCache::PersistenceDelegate {
   HostCachePersistenceManager(net::HostCache* cache,
                               PrefService* pref_service,
                               std::string pref_name,
-                              base::TimeDelta delay);
+                              base::TimeDelta delay,
+                              net::NetLog* net_log);
   virtual ~HostCachePersistenceManager();
 
   // net::HostCache::PersistenceDelegate implementation
@@ -62,6 +68,8 @@ class HostCachePersistenceManager : public net::HostCache::PersistenceDelegate {
   const base::TimeDelta delay_;
   base::OneShotTimer timer_;
 
+  const net::NetLogWithSource net_log_;
+
   SEQUENCE_CHECKER(sequence_checker_);
   base::WeakPtrFactory<HostCachePersistenceManager> weak_factory_;