Add UMA metrics for BlueZ

This adds BlueZ.ChipLost. This differs from BlueZ.AdapterLost in that
ChipLost records adapter lost specifically due to hardware
disconnection.

Corresponding CL where metrics is used: http://crosreview.com/924505

BUG=chromium:813390

Change-Id: I1a1956f6f40508b57af12c49ee4c1265c7309457
Reviewed-on: https://chromium-review.googlesource.com/930482Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Commit-Queue: Sonny Sasaka <sonnysasaka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538864}

tools/metrics/histograms/histograms.xml

@@ -8412,6 +8412,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="BlueZ.ChipLost" units="seconds">
+  <owner>sonnysasaka@chromium.org</owner>
+  <summary>
+    This is specific to Chrome OS. Records a duration of a Bluetooth adapter
+    being lost caused by hardware disconnection. This helps us better understand
+    the Bluetooth controller drop issue in the field.
+  </summary>
+</histogram>
+
 <histogram name="BlueZ.NumberOfExistingAdvertisements" units="advertisements">
   <owner>mcchou@chromium.org</owner>
   <summary>