Move the user interaction policy for FirstMeaningfulPaint UMA into renderer

third_party/WebKit/Source/core/paint/PaintTiming.cpp

Index: third_party/WebKit/Source/core/paint/PaintTiming.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintTiming.cpp b/third_party/WebKit/Source/core/paint/PaintTiming.cpp
index 3e7c53c2724f428d4395d3cc66ee5f5340e128e9..3783eb75abb63ab093464ae8f30d5df4daacbbb5 100644
--- a/third_party/WebKit/Source/core/paint/PaintTiming.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintTiming.cpp
@@ -14,6 +14,7 @@
 #include "core/page/Page.h"
 #include "core/timing/DOMWindowPerformance.h"
 #include "core/timing/Performance.h"
+#include "platform/Histogram.h"
 #include "platform/WebFrameScheduler.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
 #include "public/platform/WebLayerTreeView.h"
@@ -96,15 +97,34 @@ void PaintTiming::SetFirstMeaningfulPaintCandidate(double timestamp) {
   }
 }
 
-void PaintTiming::SetFirstMeaningfulPaint(double stamp) {
+void PaintTiming::SetFirstMeaningfulPaint(double stamp,
+                                          bool was_after_user_input) {
   DCHECK_EQ(first_meaningful_paint_, 0.0);
-  first_meaningful_paint_ = stamp;
-  TRACE_EVENT_MARK_WITH_TIMESTAMP1(
+  TRACE_EVENT_MARK_WITH_TIMESTAMP2(
       "loading,rail,devtools.timeline", "firstMeaningfulPaint",
-      TraceEvent::ToTraceTimestamp(first_meaningful_paint_), "frame",
-      GetFrame());
-  NotifyPaintTimingChanged();
-  RegisterNotifySwapTime(PaintEvent::kFirstMeaningfulPaint);
+      TraceEvent::ToTraceTimestamp(stamp), "frame", GetFrame(),
+      "afterUserInput", was_after_user_input);
+
+  // Notify FMP for UMA only if there's no user input before FMP, so that layout
+  // changes caused by user interactions wouldn't be considered as FMP.
+  if (!was_after_user_input) {
+    first_meaningful_paint_ = stamp;
+    NotifyPaintTimingChanged();
+    RegisterNotifySwapTime(PaintEvent::kFirstMeaningfulPaint);
+  }
+
+  ReportUserInputHistogram(was_after_user_input);
+}
+
+void PaintTiming::ReportUserInputHistogram(bool had_input) {
+  enum HadUserInput { kNoUserInput, kHadUserInput, kHadUserInputEnumMax };
+  DEFINE_STATIC_LOCAL(EnumerationHistogram, had_user_input_histogram,

[Bryan McQuade, 2017/06/08 17:47:12]

i'd rather not use PageLoad as the prefix here, as those are only tracked for
loads that are filtered according to page load metrics filtering policy. I don't
want to get into the habit of having other renderer-based page load metrics
either.

A couple ideas:
1. Use PageLoad.Internal namespace, which is used for internal tracking /
debugging metrics for PLM maintainers (seems right), e.g.
PageLoad.Internal.PaintTiming.HadUserInputBeforeFirstMeaningfulPaint - no need
for 'Experimental' here since there is no plan to ever promote such a metrics to
non experimental - it's just intended to be internal

2. use a totally new metrics namespace (up to you, just not PageLoad.*)

[Kunihiko Sakamoto, 2017/06/09 05:48:16]

Thanks for the suggestions, renamed to PageLoad.Internal.

+                      ("PageLoad.Experimental.Renderer.PaintTiming."
+                       "HadUserInputBeforeFirstMeaningfulPaint",
+                       kHadUserInputEnumMax));
+
+  if (GetFrame()->IsMainFrame())
+    had_user_input_histogram.Count(had_input ? kHadUserInput : kNoUserInput);
 }
 
 void PaintTiming::NotifyPaint(bool is_first_paint,