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 48eff2959d0aaf43dcac2f469cea5d33ccfdbbbb..57ef3cf613c067703cf3a32dcb4899a004990b04 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -59364,6 +59364,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>
     The result of trying to send the IPC message to a renderer process telling
     it to stop an embedded worker. Recorded in EmbeddedWorkerInstance::Stop.
+    This was previously recorded for both the IPC and Mojo service worker

[Mark P, 2017/01/05 20:11:08]

A better practice would be to rename the current
ServiceWorker.SendStopWorker.Status histogram to something like
ServiceWorker.SendStopWorker.IPC.Status, marked the current histogram as
obsolete in histograms.xml, and add the new histogram to the file.

Is there a particular reason you want to maintain the same name?

[falken, 2017/01/06 02:14:54]

The IPC implementation is already off by default (as of M56 in Beta) and will be
removed soon. We've only been maintaining it in case some big disaster is found
with the Mojo implementation that requires us to reflip the flag. Adding a new
histogram IPC.Status would be wasteful since essentially there are zero users
and we'll just remove it soon.

I think it was a mistake for Mojo to use this histogram in the first place since
there is no notion of "send an IPC message" but it's too late to fix that now
(currently it's recording OK everytime). So I suggested just adding this comment
to make clear what happened.

If this comment still doesn't sound good, I think we can just go ahead and
obsolete this histogram now and remove the logging from the code. If Mojo gets
reverted we can add a new IPC status histogram.

[Mark P, 2017/01/06 04:52:43]

Thanks for the explanation.  In this case--it's effectively obsolete already--I
think the  comment suffices.

[shimazu, 2017/01/06 04:58:23]

Thanks for your comments. I'll commit as is (ps11) for now and mark it as
obsolete when the legacy IPC path is removed.

+    implementations, but as of Jan 2017, this is only recorded for the IPC
+    implementation. This histogram will be removed after the IPC implementation
+    is removed.
   </summary>
 </histogram>