bluetooth: Add histogram for WebBluetooth actions

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 e16727c2aa6bed7f73d2ba3fc283b9ad22979c3b..3e542fa7074a37b7a1d61b4500ba5ac0932ddba7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -48304,6 +48304,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>HTTP response codes seen by Wallet client.</summary>
 </histogram>
 
+<histogram name="WebBluetooth.FunctionCall.Count" enum="WebBluetoothFunction">

[Alexei Svitkine (slow), 2015/08/03 21:59:06]

I suggest not introducing a new top-level prefix. How about
Bluetooth.WebFunctionCall.Count?

[ortuno, 2015/08/03 22:41:16]

We plan on introducing 15 new WebBluetooth histograms:
https://docs.google.com/document/d/1dchRzqqqKnpshOrPgHuTNVd-y8k5BGc3jC0jZYLhj...

The WebBluetooth prefix will help us distinguish from the more general Bluetooth
histograms.

[Alexei Svitkine (slow), 2015/08/04 15:35:03]

How about Bluetooth.Web.FunctionCall.Count then? You can then add other
Bluetooth.Web.* histograms.

[ortuno, 2015/08/04 16:01:18]

Sounds good. Done.

+  <owner>jyasskin@chromium.org</owner>
+  <owner>ortuno@chromium.org</owner>
+  <owner>scheib@chromium.org</owner>
+  <summary>
+    Counts the number of times each call to a WebBluetooth function is done.
+  </summary>
+</histogram>
+
 <histogram name="WebController.ExternalURLRequestBlocking"
     enum="IOSExternalURLRequestStatus">
   <owner>jyquinn@chromium.org</owner>
@@ -71018,6 +71027,15 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="5" label="Policy"/>
 </enum>
 
+<enum name="WebBluetoothFunction" type="int">
+  <int value="0" label="requestDevice()"/>
+  <int value="1" label="connectGATT()"/>
+  <int value="2" label="getPrimaryService()"/>
+  <int value="3" label="getCharacteristic()"/>
+  <int value="4" label="readValue()"/>

[Jeffrey Yasskin, 2015/08/03 21:51:13]

This should be Characteristic.readValue, since we also have
BluetoothGATTDescriptor.readValue(). Similarly for writeValue.

[ortuno, 2015/08/03 22:41:17]

Done.

+  <int value="5" label="writeValue()"/>
+</enum>
+
 <enum name="WebFontCacheHit" type="int">
   <int value="0" label="Miss"/>
   <int value="1" label="Hit"/>