Record shutdown type UMA

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 3202162f19148310cce022dd210d5438c94a74d0..3888ef90d95cdd2ae3d73f2b7b01ba839b515a06 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -55508,6 +55508,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Shutdown.ShutdownType" enum="ShutdownType">

[Alexei Svitkine (slow), 2016/09/14 15:56:11]

This seems to be adding a new top-level category ("Shutdown."). We generally
advise against this, unless you're planning to add lots of histograms under this
category.

Otherwise, please re-use an existing prefix.

[hashimoto, 2016/09/15 06:38:37]

Actually, "Shutdown." is not new as there are already a number of histograms
reported with this category.
(https://cs.chromium.org/chromium/src/chrome/browser/browser_shutdown.cc?q=%5C...)
The problem is that the existing histograms ("Shutdown.*.time",
"Shutdown.*.time_per_process", "Shutdown.renderers.total",
"Shutdown.renderers.slow") are not included in histograms.xml for some reason.

I thought it's better to use "Shutdown." here to make it consistent with these
existing histograms.
If we are to avoid using "Shutdown.", the only category I find appropriate is
"Chrome."
If you think it's better, I'll upload a new change with "Chrome."
WDYT?

[Alexei Svitkine (slow), 2016/09/15 16:58:56]

Ah, you are right. Looks like they're still listed in the internal
histograms.xml file in google3 and don't have any owners.

So keeping the Shutdown. prefix sounds good to me for this one. Given that
you're looking at this area, do you mind taking a look at the existing metrics
and a) moving their definitions to the open source histograms.xml and b)
removing them if they're not useful - given that they have no owners I suspect
no one has looked at them since we made the change to hide unowned histograms on
the dashboards 2-3 years ago. So I suspect they're safe to simply be removed.
(Unless you are interested in them since you're working in this area.)

+  <owner>hashimoto@chromium.org</owner>
+  <summary>The type of the last shutdown.</summary>
+</histogram>
+
 <histogram name="Signin" enum="SigninHelperFlow">
   <owner>mlerman@chromium.org</owner>
   <summary>
@@ -94502,6 +94507,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="6" label="Dark resume failed"/>
 </enum>
 
+<enum name="ShutdownType" type="int">
+  <int value="0" label="Not valid"/>
+  <int value="1" label="Window close"/>
+  <int value="2" label="Browser exit"/>
+  <int value="3" label="End session"/>

[Alexei Svitkine (slow), 2016/09/14 15:56:11]

It's not obvious to me from these what the differences between these are. What
is end session vs. browser exit? How does browser exit compare to window close?

Please add more information. You can expand on the description by putting text
within the <int> </int> tags.

[hashimoto, 2016/09/15 06:38:37]

Done.

+</enum>
+
 <enum name="SideloadUIEvents" type="int">
   <int value="0" label="Extension installed"/>
   <int value="1" label="Extension ignored"/>