Add MobileSessionShutdownType to the 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 a5f730accda40265fd50de1d44095cd790d15837..f6f649f83e594ed6c4859379dcd6c201cd4a5373 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -42582,6 +42582,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Stability.MobileSessionShutdownType"
+    enum="MobileSessionShutdownType">
+  <owner>lpromero@chromium.org</owner>
+  <owner>olivierrobin@chromium.org</owner>
+  <summary>
+    Type of the shutdown. This histogram is recorded at startup and logs a
+    sample for the previous session. A clean shutdown is one where the app
+    enters the background before being killed. Other shutdowns are all some sort
+    of crash. The absence of a crash log indicates that the app was killed by
+    the OS, normally due to memory pressure. If memory pressure is extremely
+    high, the app may not have had a chance to response to a memory warning
+    before being killed. For first launch after upgrade, the crash reports may
+    be discarded before this histogram is written to so it's not possible to
+    determine if there's a valid crash log present or not.
+  </summary>
+</histogram>
+
 <histogram name="Stars.Goog_Related" units="percent">
   <owner>yefim@chromium.org</owner>
   <summary>
@@ -62444,6 +62461,15 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="4" label="No thanks"/>
 </enum>
 
+<enum name="MobileSessionShutdownType" type="int">
+  <int value="0" label="Shutdown in background"/>
+  <int value="1" label="Shutdown in foreground; no log; no memory warning"/>
+  <int value="2" label="Shutdown in foreground; with log; no memory warning"/>
+  <int value="3" label="Shutdown in foreground; no log; with memory warning"/>
+  <int value="4" label="Shutdown in foreground; with log; with memory warning"/>
+  <int value="5" label="First launch after upgrade"/>

[Alexei Svitkine (slow), 2015/07/21 15:37:10]

Please copy this as it current appears in the internal XML. Then, it can be
updated in the same CL where you're changing the code.

Also, please send a corresponding google3 CL removing it from there. Thanks!

[Alexei Svitkine (slow), 2015/07/21 15:48:13]

Oops, I think I misread the diffs. This does look right.

+</enum>
+
 <enum name="ModuleIndex" type="int">
   <int value="0" label="chrome.dll"/>
   <int value="1" label="chrome_elf.dll"/>