Add a histogram for the peak number of WebMediaPlayer instances.

This uses a base::SingleSamplMetric to log the peak number of
instances per RenderFrame. We'll use this value to establish a
limit on the maximum allowed.

R=sandersd

Bug: 1144736
Change-Id: Ic0dac59d8682da0ea3185dcf97e7273bd9e037c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587493
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836917}

content/renderer/media/renderer_webmediaplayer_delegate.cc

@@ -48,6 +48,11 @@ RendererWebMediaPlayerDelegate::RendererWebMediaPlayerDelegate(
   is_low_end_ = base::SysInfo::IsLowEndDevice();
   idle_cleanup_timer_.SetTaskRunner(
       render_frame->GetTaskRunner(blink::TaskType::kInternalMedia));
+
+  // This corresponds to UMA_HISTOGRAM_COUNTS_1000.
+  peak_player_count_uma_ =
+      base::SingleSampleMetricsFactory::Get()->CreateCustomCountsMetric(
+          "Media.PeakWebMediaPlayerCount", 0, 1000, 50);
 }
 
 RendererWebMediaPlayerDelegate::~RendererWebMediaPlayerDelegate() {}
@@ -64,7 +69,12 @@ bool RendererWebMediaPlayerDelegate::IsFrameClosed() {
 }
 
 int RendererWebMediaPlayerDelegate::AddObserver(Observer* observer) {
-  return id_map_.Add(observer);
+  const auto result = id_map_.Add(observer);
+  if (id_map_.size() > peak_player_count_) {
+    peak_player_count_ = id_map_.size();
+    peak_player_count_uma_->SetSample(peak_player_count_);
+  }
+  return result;
 }
 
 void RendererWebMediaPlayerDelegate::RemoveObserver(int player_id) {

content/renderer/media/renderer_webmediaplayer_delegate.h

@@ -14,6 +14,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/metrics/single_sample_metrics.h"
 #include "base/single_thread_task_runner.h"
 #include "base/time/default_tick_clock.h"
 #include "base/timer/timer.h"
@@ -165,6 +166,10 @@ class CONTENT_EXPORT RendererWebMediaPlayerDelegate
   // when the idle cleanup timer should be fired more aggressively.
   bool is_low_end_;
 
+  // Records the peak player count for this render frame.
+  size_t peak_player_count_ = 0u;
+  std::unique_ptr<base::SingleSampleMetric> peak_player_count_uma_;
+
   DISALLOW_COPY_AND_ASSIGN(RendererWebMediaPlayerDelegate);
 };
 

content/renderer/media/renderer_webmediaplayer_delegate_browsertest.cc

@@ -312,6 +312,20 @@ TEST_F(RendererWebMediaPlayerDelegateTest, IdleDelegatesAreSuspended) {
   }
 }
 
+TEST_F(RendererWebMediaPlayerDelegateTest, PeakPlayerHistogram) {
+  NiceMock<MockWebMediaPlayerDelegateObserver> observer;
+  NiceMock<MockWebMediaPlayerDelegateObserver> observer2;
+  delegate_manager_->AddObserver(&observer);
+  delegate_manager_->AddObserver(&observer2);
+
+  base::HistogramTester histogram_tester;
+
+  constexpr char kHistogramName[] = "Media.PeakWebMediaPlayerCount";
+  histogram_tester.ExpectTotalCount(kHistogramName, 0);
+  delegate_manager_.reset();
+  histogram_tester.ExpectUniqueSample(kHistogramName, 2, 1);
+}
+
 #if defined(OS_ANDROID)
 
 TEST_F(RendererWebMediaPlayerDelegateTest, Histograms) {

tools/metrics/histograms/histograms_xml/media/histograms.xml

@@ -2781,6 +2781,16 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Media.PeakWebMediaPlayerCount" units="players"
+    expires_after="M95">
+  <owner>dalecurtis@google.com</owner>
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    Records the peak number of WebMediaPlayer objects per RenderFrame upon
+    RenderFrame destruction (both cleanly and via render process termination).
+  </summary>
+</histogram>
+
 <histogram name="Media.Pepper.PlayedSound" enum="Boolean"
     expires_after="2021-03-01">
   <owner>mlamouri@google.com</owner>