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 1cd9eebcbb03d2c1a5eada8404d920dec6333800..627c44eceda35052075c724ce9b16026187426cb 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6876,6 +6876,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="FileBrowser.MTPMount">
+  <owner>kinaba@chromium.org</owner>
+  <summary>
+    Chrome OS File Browser: counts the number of times MTP devices are inserted

[Ilya Sherman, 2014/05/01 21:15:24]

What is "MTP"?  Please spell out acronyms (it's fine to keep the acronym as
well, if you think it's useful).

[kinaba, 2014/05/08 04:15:41]

Done.

+    and mounted to Files.app.
+  </summary>
+</histogram>

[Ilya Sherman, 2014/05/01 21:15:24]

I strongly encourage you to design your metric with some sort of built-in
baseline.  It's much harder to interpret a raw number like "10,000" MTP devices
were mounted, vs. 0.01% or 10% of all mounted devices were MTP devices.

[kinaba, 2014/05/08 04:15:41]

Done. Changed to record the counts for all volume types.

+
 <histogram name="FileBrowser.OpeningFileType" enum="FileType">
   <obsolete>
     Deprecated 4/2013, and replaced by FileBrowser.ViewingFileType.