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 3354a5f9cc8d78098ed8f17bb4bc5b7963b55a74..ecc9810d45718ca672fc9cc1a41b23e172ed3cbd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -72208,6 +72208,8 @@ 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"/>
@@ -72382,6 +72384,8 @@ 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"/>