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 d9ccb7ac4b17da347a488e03a2ff8d66a105ce88..d7372d599a17def8213a6799ca4b477c98f34960 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -42636,6 +42636,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Precache.Freshness.Prefetch" units="seconds">
+  <owner>jamartin@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    The freshness lifetimes of the resources that were precached from the moment
+    they were fetched or revalidated as described in RFC 2616 13.2.4. Logged per
+    precache request.
+  </summary>
+</histogram>
+
 <histogram name="Precache.Latency.NonPrefetch" units="ms">
   <owner>twifkak@chromium.org</owner>
   <owner>bengr@chromium.org</owner>
@@ -42693,6 +42703,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Precache.Saved.Freshness" units="seconds">
+  <owner>jamartin@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    The freshness lifetimes of the resources that were precached and later used
+    (and thus served from the cache) as described in RFC 2616 13.2.4. This is

[twifkak, 2016/07/18 23:50:44]

nit: put "as described in RFC blah" in parens after "freshness lifetimes"; it's
a bit of a dangling modifier in its current position.

[jamartin, 2016/07/19 16:14:17]

Done.

+    computed at serving time (and thus possibly different from the precached
+    value if the cache entry was revalidated) but it is still counted from the
+    fetching (or revalidation) time. Logged per-request but only once per URL

[twifkak, 2016/07/18 23:50:44]

What do you mean by "counting from the fetching time"? AFAIK
RecordURLNonPrefetch is called for every user-initiated URL fetch (i.e. during
interactive browsing).

[jamartin, 2016/07/19 16:14:17]

I meant "fetching time" as the time when the resource was actually downloaded or
validated over the network. That means either the original precaching time or
the current request time, if the resource has been validated.

Anyway, all of this is part of the RFC spec, so I'm removing this lousy
explanation :-P

+    and precaching cycle (as Precache.Saved).
+  </summary>
+</histogram>
+
 <histogram name="PrefService.CreateProfilePrefsTime" units="ms">
   <owner>rkaplow@chromium.org</owner>
   <summary>The amount of time that elapsed during CreateProfilePrefs.</summary>