Add UMA for durations of hung render processes.

BUG=823087

Change-Id: I8f01414bbeb1472f2fe062afa5b4c66f4bf1f621
Reviewed-on: https://chromium-review.googlesource.com/972184Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544920}

content/browser/renderer_host/render_widget_host_impl.cc

@@ -1044,6 +1044,7 @@ void RenderWidgetHostImpl::StartHangMonitorTimeout(TimeDelta delay) {
   if (!hang_monitor_timeout_)
     return;
   hang_monitor_timeout_->Start(delay);
+  hang_monitor_start_time_ = clock_->NowTicks();
 }
 
 void RenderWidgetHostImpl::RestartHangMonitorTimeoutIfNecessary() {
@@ -1058,6 +1059,16 @@ bool RenderWidgetHostImpl::IsCurrentlyUnresponsive() const {
 void RenderWidgetHostImpl::StopHangMonitorTimeout() {
   if (hang_monitor_timeout_)
     hang_monitor_timeout_->Stop();
+
+  if (!hang_monitor_start_time_.is_null()) {
+    base::TimeDelta elapsed = clock_->NowTicks() - hang_monitor_start_time_;
+    const base::TimeDelta kMinimumHangTimeToReport =
+        base::TimeDelta::FromSeconds(5);
+    if (elapsed >= kMinimumHangTimeToReport)
+      UMA_HISTOGRAM_LONG_TIMES("Renderer.Hung.Duration", elapsed);
+
+    hang_monitor_start_time_ = TimeTicks();
+  }
   RendererIsResponsive();
 }
 

content/browser/renderer_host/render_widget_host_impl.h

@@ -1004,6 +1004,7 @@ class CONTENT_EXPORT RenderWidgetHostImpl
   std::unique_ptr<InputRouter> input_router_;
 
   std::unique_ptr<TimeoutMonitor> hang_monitor_timeout_;
+  base::TimeTicks hang_monitor_start_time_;
 
   std::unique_ptr<TimeoutMonitor> new_content_rendering_timeout_;
 

content/browser/renderer_host/render_widget_host_unittest.cc

@@ -15,7 +15,9 @@
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
+#include "base/test/histogram_tester.h"
 #include "base/test/scoped_feature_list.h"
+#include "base/test/simple_test_tick_clock.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
@@ -3131,4 +3133,29 @@ TEST_F(RenderWidgetHostTest, NavigateInBackgroundShowsBlank) {
   EXPECT_TRUE(host_->new_content_rendering_timeout_fired());
 }
 
+TEST_F(RenderWidgetHostTest, RendererHangRecordsMetrics) {
+  base::SimpleTestTickClock clock;
+  host_->set_clock_for_testing(&clock);
+  base::HistogramTester tester;
+
+  // RenderWidgetHost makes private the methods it overrides from
+  // InputRouterClient. Call them through the base class.
+  InputRouterClient* input_router_client = host_.get();
+
+  // Do a 3s hang. This shouldn't affect metrics.
+  input_router_client->IncrementInFlightEventCount();
+  clock.Advance(base::TimeDelta::FromSeconds(3));
+  input_router_client->DecrementInFlightEventCount(
+      InputEventAckSource::UNKNOWN);
+  tester.ExpectTotalCount("Renderer.Hung.Duration", 0u);
+
+  // Do a 17s hang. This should affect metrics.
+  input_router_client->IncrementInFlightEventCount();
+  clock.Advance(base::TimeDelta::FromSeconds(17));
+  input_router_client->DecrementInFlightEventCount(
+      InputEventAckSource::UNKNOWN);
+  tester.ExpectTotalCount("Renderer.Hung.Duration", 1u);
+  tester.ExpectUniqueSample("Renderer.Hung.Duration", 17000, 1);
+}
+
 }  // namespace content

tools/metrics/histograms/histograms.xml

@@ -72006,6 +72006,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Renderer.Hung.Duration" units="ms">
+  <owner>avi@chromium.org</owner>
+  <summary>
+    The length of time render processes are hung, in milliseconds. Note that
+    because technically speaking render processes are &quot;hung&quot; from the
+    moment an input event is sent to them until the moment that they return an
+    ACK, only hangs of minimum length 5s are recorded. Note that this combines
+    measurements from both renderer processes that recover on their own, and
+    render processes that are killed.
+  </summary>
+</histogram>
+
 <histogram name="Renderer.Hung.MobileInfoBar.UserEvent"
     enum="MobileHungRendererInfoBarEvent">
   <owner>dfalcantara@chromium.org</owner>