Add a histogram to record requestDevice outcomes.

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 a64a5d9d81b9813aed652bbaa81f648db8d5557f..fc8b7a8525f0158db88a35ec2721250ed4521ac5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -2682,6 +2682,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Bluetooth.RequestDeviceOutcome"

[Alexei Svitkine (slow), 2015/07/21 15:44:46]

Nit: Optional suggestion:

Name it: Bluetooth.RequestDevice.Outcome (both here and in the code)

This way, if you have more metrics related to requestDevice(), they can follow
the same convention.

[Jeffrey Yasskin, 2015/07/21 18:02:23]

Sounds good; thanks!

+    enum="BluetoothRequestDeviceOutcome">
+  <owner>jyasskin@chromium.org</owner>
+  <owner>ortuno@chromium.org</owner>
+  <owner>scheib@chromium.org</owner>
+  <summary>
+    Records the result of a navigator.bluetooth.requestDevice() call. Used to
+    understand what errors developers are getting so we can target efforts
+    toward the most common ones.
+  </summary>
+</histogram>
+
 <histogram name="Bookmarks.LaunchDepth">
   <owner>yfriedman@chromium.org</owner>
   <summary>
@@ -51330,6 +51342,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="8" label="Unknown or unhandler error"/>
 </enum>
 
+<enum name="BluetoothRequestDeviceOutcome" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="No Bluetooth adapter"/>
+  <int value="2" label="No RenderFrameHost for message source"/>
+  <int value="3" label="Discovery start failed"/>
+  <int value="4" label="Discovery stop failed"/>
+  <int value="5" label="No matching devices found"/>
+</enum>
+
 <enum name="BookmarksExperimentState" type="int">
   <int value="0" label="No experiment"/>
   <int value="1" label="Experiment enabled (sync)"/>