[Prerender] first contentful paint histograms.

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 ccde36a65a7663ea7e90dda0f672231c2cc3d8f2..10757592cae1762966d94f40d36ca7b281488c9c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -49372,6 +49372,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Prerender.PerceivedTTFCPRecorded" enum="BooleanEnabled">
+  <owner>droger@chromium.org</owner>
+  <owner>mattcary@chromium.org</owner>
+  <owner>pasko@chromium.org</owner>
+  <summary>
+    Whether perceived TTFCP was recorded successfully. If true, there is an

[pasko, 2016/12/20 19:33:34]

It is still a little confusing to see a reference to "perceived TTFCP" without
having Perceived.*TTFCP anywhere. Should we rename it to
Prerender.PrefetchTTFCPRecorded and update the description accordingly? Or is it
more like Prerender.TTFCPRecorded? Both of these variants sound better to me.

P.S.: yeah, pasko@ nitpicky about naming things, and not mentioning it during
offline conversation, sorry about that last part :/

[mattcary, 2016/12/21 17:08:59]

This is only active for perceived FCP. Calling it PrefetchTTFCPRecorded would
seem to imply that it should be incremented for all PrefetchTTFCP, which is not
true.

[pasko, 2016/12/21 18:39:09]

The word "perceived" does not obviously translate to something equivalent to
"For Prerender, but also only if swap-in happened". I had to read the code to
figure this out. For people not familiar with prerender, it will be all cryptic.

How about "Recorded for each Prerendered WebContents that reaches the First
Contentful Paint. Records True for prerenders that were _used_, False
otherwise.", which would be named like "Prerender.IsSwappedInWhenReachedTTFCP".

It could be I am still missing a few possibilities. Please correct me.

[mattcary, 2016/12/22 10:49:07]

ptal

+    associated PrefetchTTFCP that records the TTFCP from the swapped-in
+    navigation start. If false, no PrefetchTTFCP was recorded.
+  </summary>
+</histogram>
+
 <histogram name="Prerender.PercentLoadDoneAtSwapin">
   <owner>pasko@chromium.org</owner>
   <summary>
@@ -49397,6 +49408,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Prerender.PrefetchTTFCP" units="ms">
+  <owner>droger@chromium.org</owner>
+  <owner>mattcary@chromium.org</owner>
+  <owner>pasko@chromium.org</owner>
+  <summary>
+    Time to first contentful paint (TTFCP) for navigations related to prefetch
+    (including prerender, no-state prefetch, and associated experiments). This
+    measures user-visible TTFCP. For no-state prefetch this is standard
+    navigation-to-FCP; for prerender this is the time from navigation start when
+    the prerender is swapped in to FCP.
+  </summary>
+</histogram>
+
 <histogram name="Prerender.PrerenderCountOf3Max">
   <owner>pasko@chromium.org</owner>
   <summary>
@@ -113183,6 +113207,7 @@ value.
              prefetched pages (bias)."/>
   <suffix name="Warm" label="Prefetch skips revalidation."/>
   <affected-histogram name="Prerender.NoStatePrefetchTTFCP"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="PrerenderPrefetchMainResourceType" separator=".">
@@ -113191,6 +113216,21 @@ value.
   <affected-histogram name="Prerender.NoStatePrefetchTTFCP.Cold"/>
   <affected-histogram name="Prerender.NoStatePrefetchTTFCP.Reference"/>
   <affected-histogram name="Prerender.NoStatePrefetchTTFCP.Warm"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Reference"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm"/>
+</histogram_suffixes>
+
+<histogram_suffixes name="PrerenderPrefetchPaintVisibility" separator=".">
+  <suffix name="Hidden" label="Page was hidden during rendering."/>
+  <suffix name="Visible" label="Page visible for all of rendering."/>
+  <affected-histogram name="Prerender.PerceivedTTFCPRecorded"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold.Cacheable"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold.NoStore"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Reference.Cacheable"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Reference.NoStore"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm.Cacheable"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm.NoStore"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="PrerenderSource" ordering="prefix">
@@ -113244,7 +113284,23 @@ value.
   <affected-histogram name="Prerender.PerceivedPLTMatchedComplete"/>
   <affected-histogram name="Prerender.PerceivedPLTWindowed"/>
   <affected-histogram name="Prerender.PerceivedPLTWindowNotMatched"/>
+  <affected-histogram name="Prerender.PerceivedTTFCPRecorded.Hidden"/>
+  <affected-histogram name="Prerender.PerceivedTTFCPRecorded.Visible"/>
   <affected-histogram name="Prerender.PercentLoadDoneAtSwapin"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold.Cacheable.Hidden"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold.Cacheable.Visible"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold.NoStore.Hidden"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Cold.NoStore.Visible"/>
+  <affected-histogram
+      name="Prerender.PrefetchTTFCP.Reference.Cacheable.Hidden"/>
+  <affected-histogram
+      name="Prerender.PrefetchTTFCP.Reference.Cacheable.Visible"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Reference.NoStore.Hidden"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Reference.NoStore.Visible"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm.Cacheable.Hidden"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm.Cacheable.Visible"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm.NoStore.Hidden"/>
+  <affected-histogram name="Prerender.PrefetchTTFCP.Warm.NoStore.Visible"/>
   <affected-histogram name="Prerender.PrerenderNotSwappedInPLT"/>
   <affected-histogram name="Prerender.PrerendersPerSessionCount"/>
   <affected-histogram name="Prerender.SimulatedLocalBrowsingBaselinePLT"/>