[net/dns] Instrument DnsConfigService to measure performance and failures.

net/dns/dns_config_service.cc

Index: net/dns/dns_config_service.cc
diff --git a/net/dns/dns_config_service.cc b/net/dns/dns_config_service.cc
index bff1fc709f8df5d1b9f1e26f75dccf8e73b97573..f17e32b73048a08a4ec84f2ac1c84eeb2ef1795c 100644
--- a/net/dns/dns_config_service.cc
+++ b/net/dns/dns_config_service.cc
@@ -5,6 +5,7 @@
 #include "net/dns/dns_config_service.h"
 
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/values.h"
 #include "net/base/ip_endpoint.h"
 
@@ -104,6 +105,12 @@ void DnsConfigService::Watch(const CallbackType& callback) {
 
 void DnsConfigService::InvalidateConfig() {
   DCHECK(CalledOnValidThread());
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (!last_invalidate_config_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.ConfigNotifyInterval",
+                             now - last_invalidate_config_time_);
+  }
+  last_invalidate_config_time_ = now;
   if (!have_config_)
     return;
   have_config_ = false;
@@ -112,6 +119,12 @@ void DnsConfigService::InvalidateConfig() {
 
 void DnsConfigService::InvalidateHosts() {
   DCHECK(CalledOnValidThread());
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (!last_invalidate_hosts_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.HostsNotifyInterval",
+                             now - last_invalidate_hosts_time_);
+  }
+  last_invalidate_hosts_time_ = now;
   if (!have_hosts_)
     return;
   have_hosts_ = false;
@@ -122,10 +135,17 @@ void DnsConfigService::OnConfigRead(const DnsConfig& config) {
   DCHECK(CalledOnValidThread());
   DCHECK(config.IsValid());
 
+  bool changed = false;
   if (!config.EqualsIgnoreHosts(dns_config_)) {
     dns_config_.CopyIgnoreHosts(config);
     need_update_ = true;
+    changed = true;
   }
+  if (!changed && !last_sent_empty_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.UnchangedConfigInterval",
+                             base::TimeTicks::Now() - last_sent_empty_time_);
+  }
+  UMA_HISTOGRAM_BOOLEAN("AsyncDNS.ConfigChange", changed);
 
   have_config_ = true;
   if (have_hosts_)
@@ -135,10 +155,17 @@ void DnsConfigService::OnConfigRead(const DnsConfig& config) {
 void DnsConfigService::OnHostsRead(const DnsHosts& hosts) {
   DCHECK(CalledOnValidThread());
 
+  bool changed = false;
   if (hosts != dns_config_.hosts) {
     dns_config_.hosts = hosts;
     need_update_ = true;
+    changed = true;
+  }
+  if (!changed && !last_sent_empty_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.UnchangedHostsInterval",
+                             base::TimeTicks::Now() - last_sent_empty_time_);
   }
+  UMA_HISTOGRAM_BOOLEAN("AsyncDNS.HostsChange", changed);
 
   have_hosts_ = true;
   if (have_config_)
@@ -178,6 +205,7 @@ void DnsConfigService::OnTimeout() {
   need_update_ = true;
   // Empty config is considered invalid.
   last_sent_empty_ = true;
+  last_sent_empty_time_ = base::TimeTicks::Now();
   callback_.Run(DnsConfig());
 }