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 42aa0be767417fb91ad3a0eae0b44d7b7fcd87cb..eef81615530fd996c8f24b33f4348fd0599f0e8b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -72306,6 +72306,8 @@ 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 (Only built via GN, not GYP) -->
+
   <int value="1615384" label="alert_notification_control_point"/>
   <int value="4531384" label="date_of_birth"/>
   <int value="22829753" label="barometric_pressure_trend"/>
@@ -72480,6 +72482,8 @@ 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 (Only built via GN, not GYP) -->
+
   <int value="7464675" label="pulse_oximeter"/>
   <int value="26695985" label="fe20"/>
   <int value="35226455" label="fe44"/>