Add a histogram to track how many server configs has been persisted

net/http/http_server_properties_manager.cc

Index: net/http/http_server_properties_manager.cc
diff --git a/net/http/http_server_properties_manager.cc b/net/http/http_server_properties_manager.cc
index 4130a57a4872d81799c523ba4d5507efce24e102..884d1ff393fd1b57529ee50eedea4d1bcb49c51f 100644
--- a/net/http/http_server_properties_manager.cc
+++ b/net/http/http_server_properties_manager.cc
@@ -775,6 +775,9 @@ void HttpServerPropertiesManager::UpdateCacheFromPrefsOnNetworkThread(
 
   http_server_properties_impl_->SetServerNetworkStats(server_network_stats_map);
 
+  UMA_HISTOGRAM_COUNTS("Net.CountOfQuicServerInfos",

[Alexei Svitkine (slow), 2017/02/23 18:23:41]

Nit: We now recommend to use UMA_HISTOGRAM_COUNTS_<max>() macros instead.

UMA_HISTOGRAM_COUNTS() corresponds to UMA_HISTOGRAM_COUNTS_1M() - so if that's
appropriate use that, but I suspect in this case you might have better results
with a smaller maximum like 10k or something.

[Zhongyi Shi, 2017/02/23 20:36:22]

Done.

+                       quic_server_info_map->size());
+
   http_server_properties_impl_->SetQuicServerInfoMap(quic_server_info_map);
 
   // Update the prefs with what we have read (delete all corrupted prefs).