Here's how to reproduce this issue:

1. Restart chrome
2. Go to https://webbluetoothcg.github.io/demos/playbulb-candle/
3. Click on "Connect" button and pick the candle device nearby you
4. Go to chrome://histograms
5. Look for "bluetooth.web"


Histogram: Bluetooth.Web.FunctionCall.Count recorded 11 samples, average = 2.3 (flags = 0x1)
0  ------------------------------------O                                     (2 = 18.2%)
1  ------------------O                                                       (1 = 9.1%) {18.2%}
2  ------------------------------------O                                     (2 = 18.2%) {27.3%}
3  ------------------------------------------------------------------------O (4 = 36.4%) {45.5%}
4  ------------------------------------O                                     (2 = 18.2%) {81.8%}
5  ... 


Histogram: Bluetooth.Web.RequestDevice.Outcome recorded 1 samples, average = 0.0 (flags = 0x1)
0  ------------------------------------------------------------------------O (1 = 100.0%)
1  ... 


There are indeed 2 requestDevice calls while there is only 1 outcome.

I believe this is because RecordWebBluetoothFunctionCall(UMAWebBluetoothFunction::REQUEST_DEVICE) is called in BluetoothDispatcherHost::OnRequestDevice AND BluetoothDispatcherHost::OnRequestDeviceImpl

Argh. Thanks for looking into it! I've sent out a patch for review: http://crrev.com/1843643002

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d2c5f54b9da878b08150552525e0a6228d8045cd

commit d2c5f54b9da878b08150552525e0a6228d8045cd
Author: ortuno <ortuno@chromium.org>
Date: Tue Mar 29 17:57:49 2016

bluetooth: remove duplicate histograming of request device.

BUG= 598120 

Review URL: https://codereview.chromium.org/1843643002

Cr-Commit-Position: refs/heads/master@{#383766}

[modify] https://crrev.com/d2c5f54b9da878b08150552525e0a6228d8045cd/content/browser/bluetooth/bluetooth_dispatcher_host.cc