Web MIDI: add a new UMA entry for the final result code

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 160a864c0f9d30adec864a1a3f7f0cb642307612..14965012733de908c58e10b7c56550acc5d051fb 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -17371,6 +17371,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Midi.ResultOnShutdown" enum="MidiResult">

[Alexei Svitkine (slow), 2015/07/09 17:11:27]

This seems to be introducing a new top-level prefix. Can it re-use an existing
one instead?

For example, Media.Midi.ResultOnShutdown?

[Takashi Toyoshima, 2015/07/09 17:43:30]

Done.

+  <owner>toyoshim@chromium.org</owner>
+  <summary>The final status of MidiManager on browser shutdown.</summary>
+</histogram>
+
 <histogram name="Mist.SwitchResult" enum="MistSwitchResult">
   <owner>benchan@chromium.org</owner>
   <summary>
@@ -61667,6 +61672,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1" label="Not muted"/>
 </enum>
 
+<enum name="MidiResult" type="int">
+  <int value="0" label="Not initialized"/>
+  <int value="1" label="Successfully initialized"/>
+  <int value="2" label="Not supported"/>
+  <int value="3" label="Generic initialization error"/>
+</enum>
+
 <enum name="MigrationNssToPemNetworkTypes" type="int">
   <int value="0" label="EAP"/>
   <int value="1" label="OpenVPN"/>