tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 29bd28575de8e128826d0575f666c29494cc543e..cf51123d79ce65c5c0abd44ebe284bb42f9ee107 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -38032,6 +38032,45 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Experimental.PaintTiming.FirstMeaningfulPaintStatus"
+    enum="FirstMeaningfulPaintStatus">
+  <owner>ksakamoto@chromium.org</owner>
+  <summary>
+    Records whether the First Meaningful Paint metric was reported for the page

[Ilya Sherman, 2016/08/10 05:42:36]

It would be helpful to link to some document explaining what the "first
meaningful paint" is, exactly.

[Kunihiko Sakamoto, 2016/08/10 07:43:09]

Done.

+    load, or why it wasn't if not.
+  </summary>
+</histogram>
+
+<histogram
+    name="PageLoad.Experimental.PaintTiming.FirstMeaningfulPaintToNetworkStable"
+    units="ms">
+  <owner>ksakamoto@chromium.org</owner>
+  <summary>
+    Measures the time between when the first meaningful paint was computed to
+    have happened, and when we actually logged the metric.

[Ilya Sherman, 2016/08/10 05:42:36]

"when we actually logged the metric" doesn't really give a clear explanation of
why that's relevant.  Why is this metric relevant?  Please clarify in the
description.

[Kunihiko Sakamoto, 2016/08/10 07:43:09]

Done.

+  </summary>
+</histogram>
+
+<histogram
+    name="PageLoad.Experimental.PaintTiming.NavigationToFirstMeaningfulPaint"
+    units="ms">
+  <owner>ksakamoto@chromium.org</owner>
+  <summary>
+    Measures the time from navigation timing's navigation start to the time the
+    page's primary content is painted, for main frame documents.
+  </summary>
+</histogram>
+
+<histogram
+    name="PageLoad.Experimental.PaintTiming.ParseStartToFirstMeaningfulPaint"

[Ilya Sherman, 2016/08/10 05:42:36]

Hmm, why is it useful to measure both the duration from parse start to FMP and
from navigation to FMP?  Is the duration between navigation and parse start not
already measured in other histograms?

[Kunihiko Sakamoto, 2016/08/10 07:43:09]

This can be less-noisy optimization target for non-navigation based
improvements. csharrison@ suggested this earlier in this review (#53), so he
might have some more context.

[Charlie Harrison, 2016/08/10 12:17:07]

Yeah in general it is a challenge of the loading team to get stable metrics,
especially with data from some of the early channels. Cutting out a
(significant) time in the loading pipeline de-noises our experiments that only
take affect once the page starts parsing HTML (which is the majority of them).

[Ilya Sherman, 2016/08/10 18:48:09]

So, would it make sense to *only* measure the duration from parse start time,
and not to measure the duration from navigation?

[Charlie Harrison, 2016/08/10 19:12:20]

It would, except for the fact that some optimizations do take into account the
navigation (speculative prefetch, plznavigate, preconnect, http2 push, etc). If
that weren't the case then yeah cutting out navigation time wholesale would be
fine.

+    units="ms">
+  <owner>ksakamoto@chromium.org</owner>
+  <summary>
+    Measures the time from when the HTML parser started, to the time the page's
+    primary content is painted, for main frame documents.
+  </summary>
+</histogram>
+
 <histogram name="PageLoad.Internal.ClientRedirect.FirstPaintToNavigation"
     units="ms">
   <owner>bmcquade@chromium.org</owner>
@@ -78864,6 +78903,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="20" label=".log"/>
 </enum>
 
+<enum name="FirstMeaningfulPaintStatus" type="int">
+  <int value="0" label="First meaningful paint recorded successfully."/>
+  <int value="1" label="The page was backgrounded."/>
+  <int value="2" label="User left the page before network stable."/>
+  <int value="3"
+      label="User interaction happened before first meaningful paint."/>

[Ilya Sherman, 2016/08/10 05:42:36]

These labels are quite long, and will be hard to read as the left-hand column in
a tabular view.  Could you shorten them somewhat, without reducing their clarity
in context?

[Kunihiko Sakamoto, 2016/08/10 07:43:09]

Done.

+</enum>
+
 <enum name="FlashNavigateUsageType" type="int">
   <int value="0" label="Rejected because of Authorization header."/>
   <int value="1" label="Rejected because of Cache-Control header."/>