Add Mist.SwitchResult histogram.

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 edc2203d6df388fafcfba874940df1753b4b15ee..828698b13e6d818093e55b1b2a4296dc71405378 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6224,6 +6224,13 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Mist.SwitchResult" enum="MistSwitchResult">
+  <summary>
+    The result (e.g. success or the type of failure) of a modem interface switch
+    operation performed by mist on Chrome OS.
+  </summary>
+</histogram>
+
 <histogram name="Mouse.PointerSensitivity.Changed" enum="PointerSensitivity">
   <summary>
     Tracks mouse sensitivity setting changes by the user. This replaces the old
@@ -22863,6 +22870,11 @@ other types of suffix sets.
   <int value="3" label="kInvalidPlayerState"/>
 </enum>
 
+<enum name="MistSwitchResult" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="Failure"/>

[Ben Chan, 2013/09/16 23:37:32]

mist currently doesn't support more fine-grained failure types, but I'm planning
to add that later

+</enum>
+
 <enum name="MobileSessionCallerApp" type="int">
   <int value="0" label="Google Search"/>
   <int value="1" label="GMail"/>