Added PerSession UMA metrics for smoothness

Reported smoothness UKM metrics are also reported to UMA, under
"Graphics.Smoothness.PerSession"

Bug: 1115141
Change-Id: I5c82dd78a44aa06fde63ebde11bcc953464b9548
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2547394Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833010}

chrome/browser/page_load_metrics/observers/core/ukm_page_load_metrics_observer.cc

@@ -9,6 +9,8 @@
 #include <vector>
 
 #include "base/feature_list.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/timer/elapsed_timer.h"
 #include "base/trace_event/common/trace_event_common.h"
 #include "cc/metrics/ukm_smoothness_data.h"
@@ -987,6 +989,16 @@ void UkmPageLoadMetricsObserver::RecordSmoothnessMetrics() {
       .SetAboveThreshold(smoothness_data.above_threshold)
       .SetWorstCase(smoothness_data.worst_smoothness)
       .Record(ukm::UkmRecorder::Get());
+
+  UMA_HISTOGRAM_PERCENTAGE(
+      "Graphics.Smoothness.PerSession.AveragePercentDroppedFrames",
+      smoothness_data.avg_smoothness);
+  UMA_HISTOGRAM_PERCENTAGE(
+      "Graphics.Smoothness.PerSession.95pctPercentDroppedFrames_1sWindow",
+      smoothness_data.percentile_95);
+  UMA_HISTOGRAM_PERCENTAGE(
+      "Graphics.Smoothness.PerSession.MaxPercentDroppedFrames_1sWindow",
+      smoothness_data.worst_smoothness);
 }
 
 void UkmPageLoadMetricsObserver::RecordMobileFriendlinessMetrics() {

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -6186,6 +6186,55 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram
+    name="Graphics.Smoothness.PerSession.95pctPercentDroppedFrames_1sWindow"
+    units="%" expires_after="2021-11-18">
+  <owner>sadrul@chromium.org</owner>
+  <owner>graphics-dev@chromium.org</owner>
+  <summary>
+    Tracks the 95th percentile of dropped frames percent of a sliding window of
+    1 second. The metric is reported once per page-load when the page closes. If
+    there are fewer than 20 sliding windows for calculating 95th percentile, the
+    max value will be used instead of 95th percentile.
+
+    PercentDroppedFrames is measured by tracking the number of frames which were
+    not displayed on screen out of the total number of frames expected to be
+    produced and displayed. In other words, the lower this number is, the
+    smoother experience.
+  </summary>
+</histogram>
+
+<histogram name="Graphics.Smoothness.PerSession.AveragePercentDroppedFrames"
+    units="%" expires_after="2021-11-18">
+  <owner>sadrul@chromium.org</owner>
+  <owner>graphics-dev@chromium.org</owner>
+  <summary>
+    Tracks the percent of dropped frames. The metric is reported once per
+    page-load when the page closes.
+
+    AveragePercentDroppedFrames is measured by tracking the number of frames
+    which were not displayed on screen out of the total number of frames
+    expected to be produced and displayed. In other words, the lower this number
+    is, the smoother experience.
+  </summary>
+</histogram>
+
+<histogram
+    name="Graphics.Smoothness.PerSession.MaxPercentDroppedFrames_1sWindow"
+    units="%" expires_after="2021-11-18">
+  <owner>sadrul@chromium.org</owner>
+  <owner>graphics-dev@chromium.org</owner>
+  <summary>
+    Tracks the Max of dropped frames percent of a sliding window of 1 second.
+    The metric is reported once per page-load when the page closes.
+
+    PercentDroppedFrames is measured by tracking the number of frames which were
+    not displayed on screen out of the total number of frames expected to be
+    produced and displayed. In other words, the lower this number is, the
+    smoother experience.
+  </summary>
+</histogram>
+
 <histogram name="Graphics.Smoothness.Stale" units="ms"
     expires_after="2021-11-01">
   <owner>sadrul@chromium.org</owner>