bluetooth: Create bluetooth_metrics_hash tool.

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 7b4731e6491bdbc200d30de7ecb7fbd264ecd40b..d6f7b09728785bfb3245afcb5c6fc862bad17bc2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -71765,6 +71765,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </enum>
 
 <enum name="GATTCharacteristicHash" type="int">
+<!-- Hash values can be produced using tool: bluetooth_metrics_hash -->

[Jeffrey Yasskin, 2016/04/15 21:23:58]

Does `ninja bluetooth_metrics_hash` build the tool, or do folks need the whole
path? You should probably mention that it's gn-only.

[scheib, 2016/04/15 22:45:22]

Yes, just the short name.
Done: GN only mentioned.

+
   <int value="1615384" label="alert_notification_control_point"/>
   <int value="4531384" label="date_of_birth"/>
   <int value="22829753" label="barometric_pressure_trend"/>
@@ -71932,6 +71934,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </enum>
 
 <enum name="GATTServiceHash" type="int">
+<!-- Hash values can be produced using tool: bluetooth_metrics_hash -->
+
   <int value="7464675" label="pulse_oximeter"/>
   <int value="81094401" label="link_loss"/>
   <int value="217781951" label="human_interface_device"/>