Add metrics for DelayNavigationThrottle

chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc

Index: chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc
diff --git a/chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc b/chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc
index 503641accdcb8e77444713f3069cf4450be5a4a5..bc32e8f18d5907286025bdc6205b580ab1bb48a5 100644
--- a/chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc
+++ b/chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.cc
@@ -6,6 +6,7 @@
 
 #include "base/memory/ptr_util.h"
 #include "base/metrics/field_trial_params.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/rand_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/profiles/profile.h"
@@ -15,6 +16,13 @@
 
 namespace {
 
+const char kHistogramNavigationDelaySpecified[] =
+    "DelayNavigationThrottle.Delay.Specified";
+const char kHistogramNavigationDelayActual[] =
+    "DelayNavigationThrottle.Delay.Actual";
+const char kHistogramNavigationDelayDelta[] =
+    "DelayNavigationThrottle.Delay.Delta";
+
 base::TimeDelta GetNavigationDelayFromParams() {
   double delay_probability = base::GetFieldTrialParamByFeatureAsDouble(
       kDelayNavigationFeature,
@@ -100,6 +108,8 @@ DelayNavigationThrottle::~DelayNavigationThrottle() {}
 
 content::NavigationThrottle::ThrottleCheckResult
 DelayNavigationThrottle::WillStartRequest() {
+  UMA_HISTOGRAM_TIMES(kHistogramNavigationDelaySpecified, navigation_delay_);
+  delay_start_time_ = base::TimeTicks::Now();
   task_runner_->PostDelayedTask(
       FROM_HERE,
       base::Bind(&DelayNavigationThrottle::OnDelayComplete,
@@ -109,5 +119,9 @@ DelayNavigationThrottle::WillStartRequest() {
 }
 
 void DelayNavigationThrottle::OnDelayComplete() {
+  base::TimeDelta actual_delay = base::TimeTicks::Now() - delay_start_time_;
+  base::TimeDelta delay_delta = actual_delay - navigation_delay_;
+  UMA_HISTOGRAM_TIMES(kHistogramNavigationDelayActual, actual_delay);
+  UMA_HISTOGRAM_TIMES(kHistogramNavigationDelayDelta, delay_delta.magnitude());

[Charlie Harrison, 2017/04/05 16:54:37]

if actual_delay < navigation_delay_ this could be problematic. If we expect this
to not happen very often, could we just let negative values clamp to 0?

[Bryan McQuade, 2017/04/05 20:11:05]

copying the relevant part of my general reply here:

I'm hesitant to clamp to zero as this prevents us from seeing the delta in cases
where it's negative. The goal of the delta histo is just to give us insight into
the accuracy of the delays overall.

   navigation_handle()->Resume();
 }