FirstMeaningfulPaint UMA

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index 9f927511dcde2c2122bcbf117d29eded4a9bbb0d..db082244f8b7d27e015ba02cf758acd6277b6e6a 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -229,6 +229,8 @@ void DispatchObserverTimingCallbacks(PageLoadMetricsObserver* observer,
     observer->OnFirstImagePaint(new_timing, extra_info);

[Bryan McQuade, 2016/07/29 15:02:26]

there's also some logic in this file that validates that the various events in a
PageLoadTiming are in order (see the calls to EventsInOrder). Can you add a
call, something like:

if (!EventsInOrder(timing.first_paint, timing.first_meaningful_paint)) {
  NOTREACHED() << ...;
  return false;
}

and there's some similar code in the test harness that makes sure timing data is
populated correctly which you'll need to update as well.

[Kunihiko Sakamoto, 2016/08/01 08:52:06]

Done.
The only ordering we can guarantee is FP <= FMP.

[Kunihiko Sakamoto, 2016/08/02 03:19:37]

Um, actually that wasn't true...
If the page has no foreground elements, FMP may be first (empty) paint where FP
is not recorded.

In patch set 4 I've made FMPDetector skip background-only paints.

   if (new_timing.first_contentful_paint && !last_timing.first_contentful_paint)
     observer->OnFirstContentfulPaint(new_timing, extra_info);
+  if (new_timing.first_meaningful_paint && !last_timing.first_meaningful_paint)
+    observer->OnFirstMeaningfulPaint(new_timing, extra_info);
   if (new_timing.parse_start && !last_timing.parse_start)
     observer->OnParseStart(new_timing, extra_info);
   if (new_timing.parse_stop && !last_timing.parse_stop)