UMA stats for MTP file system in Chrome OS Files.app.

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 382be8639c4e797982dfdd9cd649af8c11efad74..298eecb42fbf9c3fd97334e5702fc79400b12bdd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -7053,6 +7053,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="FileBrowser.VolumeType" enum="FileManagerVolumeType">
+  <owner>kinaba@chromium.org</owner>
+  <summary>
+    Chrome OS File Browser: counts the number of times volumes are mounted for
+    each volume type.
+  </summary>
+</histogram>
+
 <histogram name="GCM.CheckinRequestStatus" enum="GCMCheckinRequestStatus">
   <owner>juyik@chromium.org</owner>
   <summary>Status code of the outcome of a GCM checkin request.</summary>
@@ -35089,6 +35097,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="6" label="Error"/>
 </enum>
 
+<enum name="FileManagerVolumeType" type="int">
+  <int value="0" label="Google Drive"/>
+  <int value="1" label="Download Folder"/>
+  <int value="2" label="Removable Disk"/>
+  <int value="3" label="Archive File"/>
+  <int value="4" label="Cloud Device"/>
+  <int value="5" label="FileSystemProvider API"/>
+  <int value="6" label="MTP (Media Transfer Protocol) Device"/>
+</enum>
+
 <enum name="FileType" type="int">
   <int value="0" label="other"/>
   <int value="1" label=".doc"/>