time metric: record elapsed time from when the backgrounded and purged renderer is foregrounded unti

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 1dcaaa6f25a0819ac9b32f3e6748c033b2c1c9cf..a43966ec8035e3f0460ca14c44ccc26aed9c73a3 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -896,6 +896,8 @@ void RenderThreadImpl::Init(
   record_purge_suspend_growth_metric_closure_.Reset(
       base::Bind(&RenderThreadImpl::RecordPurgeAndSuspendMemoryGrowthMetrics,
                  base::Unretained(this)));
+  record_first_active_paint_ = true;
+  foregrounded_time_ = base::TimeTicks::Now();
 
   base::MemoryCoordinatorClientRegistry::GetInstance()->Register(this);
 
@@ -1653,6 +1655,7 @@ void RenderThreadImpl::OnProcessBackgrounded(bool backgrounded) {
     record_purge_suspend_growth_metric_closure_.Reset(
         base::Bind(&RenderThreadImpl::RecordPurgeAndSuspendMemoryGrowthMetrics,
                    base::Unretained(this)));
+    foregrounded_time_ = base::TimeTicks::Now();
   }
 }
 
@@ -1679,6 +1682,7 @@ void RenderThreadImpl::OnProcessPurgeAndSuspend() {
   GetRendererScheduler()->DefaultTaskRunner()->PostDelayedTask(
       FROM_HERE, record_purge_suspend_metric_closure_.callback(),
       base::TimeDelta::FromSeconds(15));
+  record_first_active_paint_ = false;
 }
 
 // TODO(tasak): Replace the following GetMallocUsage() with memory-infra
@@ -2442,4 +2446,14 @@ void RenderThreadImpl::OnRendererInterfaceRequest(
   renderer_binding_.Bind(std::move(request));
 }
 
+void RenderThreadImpl::OnPostWidgetUpdateVisualState() {
+  if (record_first_active_paint_)

[esprehn, 2017/01/25 03:22:17]

Can we put all of this code into RenderWidget instead and have it query the
times from the RenderThread?

[tasak, 2017/01/26 09:39:40]

I moved the code into RenderWidget.

+    return;
+
+  record_first_active_paint_ = true;
+  base::TimeDelta sample = base::TimeTicks::Now() - foregrounded_time_;
+  UMA_HISTOGRAM_TIMES("PurgeAndSuspend.Experimental.TimeToFirstActivePaint",
+                      sample);
+}
+
 }  // namespace content