[scheduler] Report background timer throttling intervention.

third_party/WebKit/Source/platform/scheduler/renderer/web_view_scheduler_impl.cc

Index: third_party/WebKit/Source/platform/scheduler/renderer/web_view_scheduler_impl.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/renderer/web_view_scheduler_impl.cc b/third_party/WebKit/Source/platform/scheduler/renderer/web_view_scheduler_impl.cc
index f7ba68c71c706abc2f5cb8692294400ea498420e..2072b56ab50f56f9e5aa82664444ab38d0d0b9d6 100644
--- a/third_party/WebKit/Source/platform/scheduler/renderer/web_view_scheduler_impl.cc
+++ b/third_party/WebKit/Source/platform/scheduler/renderer/web_view_scheduler_impl.cc
@@ -5,6 +5,7 @@
 #include "platform/scheduler/renderer/web_view_scheduler_impl.h"
 
 #include "base/logging.h"
+#include "base/strings/stringprintf.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/scheduler/base/virtual_time_domain.h"
 #include "platform/scheduler/child/scheduler_tqm_delegate.h"
@@ -19,6 +20,10 @@ namespace scheduler {
 namespace {
 
 const double kBackgroundBudgetAsCPUFraction = .01;
+// Given that we already align timers to 1Hz, do not report throttling if
+// it is under 3s.
+constexpr base::TimeDelta kMinimalThrottlingDurationToReport =

[Sami, 2016/11/04 17:51:49]

kMinimalThrottlingDurationToReport since we report about other types of
throttling too.

[altimin, 2016/11/07 17:25:30]

Did you mean kMinimalBackgroundThrottlingDurationToReport? :)

+    base::TimeDelta::FromSeconds(3);
 
 }  // namespace
 
@@ -198,5 +203,20 @@ bool WebViewSchedulerImpl::IsAudioPlaying() const {
   return is_audio_playing_;
 }
 
+void WebViewSchedulerImpl::OnThrottlingReported(
+    base::TimeDelta throttling_duration) {
+  if (throttling_duration < kMinimalThrottlingDurationToReport)
+    return;
+
+  std::string message = base::StringPrintf(
+      "Background timers take too long to run on this page. "

[Sami, 2016/11/04 17:51:49]

To rephrase a bit:

"Timer tasks have used too much CPU time while the page was in the background.
As a result, they have been deferred by NN seconds. See ... for more details."

[altimin, 2016/11/07 17:25:30]

Done.

+      "They have been throttled for %.3f seconds. "
+      "See https://www.chromestatus.com/feature/6172836527865856 "
+      " for more details",
+      throttling_duration.InSecondsF());
+
+  intervention_reporter_->ReportIntervention(WebString::fromUTF8(message));

[Sami, 2016/11/04 17:51:49]

Is this potentially spammy? I wonder if we should just print this once per
navigation. I don't think the developers need notification for each and every
instance.

[altimin, 2016/11/07 17:25:30]

Done.

+}
+
 }  // namespace scheduler
 }  // namespace blink