SmartLock: Fix the name of the eligible devices count histogram.

This is actually the count of enabled devices, not eligible devices. The existing metric, EligibleDevicesCount, will be logged to in a follow-up CL.

R=hansberry@chromium.org

Bug: 831371
Test: none
Change-Id: I38e8a57678f8a9b9d9c23186431147b0961fad43
Reviewed-on: https://chromium-review.googlesource.com/1031182
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555593}

chrome/browser/chromeos/login/easy_unlock/easy_unlock_service.cc

@@ -668,7 +668,7 @@ EasyUnlockAuthEvent EasyUnlockService::GetPasswordAuthEvent() const {
 void EasyUnlockService::SetProximityAuthDevices(
     const AccountId& account_id,
     const cryptauth::RemoteDeviceList& remote_devices) {
-  UMA_HISTOGRAM_COUNTS_100("SmartLock.EligibleDevicesCount",
+  UMA_HISTOGRAM_COUNTS_100("SmartLock.EnabledDevicesCount",
                            remote_devices.size());
 
   if (remote_devices.size() == 0) {

tools/metrics/histograms/histograms.xml

@@ -88896,7 +88896,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>
     A count of the number of eligible SmartLock devices which can be used to
     unlock the user's Chromebook. Logged each time the list of eligible devices
-    is updated.
+    is updated. TODO(jhawkins): Log this again once we send this data from
+    eligible phones.
+  </summary>
+</histogram>
+
+<histogram name="SmartLock.EnabledDevicesCount" units="devices">
+  <owner>jhawkins@chromium.org</owner>
+  <summary>
+    A count of the number of SmartLock devices which the user has enabled to
+    unlock the user's Chromebook, i.e., the device connected to in the SmartLock
+    setup flow. Logged each time the list of eligible devices is updated.
   </summary>
 </histogram>