If location services are turned off, have the BT chooser prompt the user to turn them on.

chrome/android/java/strings/android_chrome_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- android_chrome_strings.grd contains strings for Chrome for Android.
 
 FAQ:
   - How do I add, change, or remove a string?
       Just update this file.
   - Translations will happen automatically??
       Yes, indeed. Just add your string before the branch point and
       make the description good.
@@ skipping 1174 matching lines @@
       <message name="IDS_BLUETOOTH_NOT_FOUND" desc="The message to show when no items were found during Bluetooth device scanning.">
         No bluetooth devices found. <ph name="BEGIN_LINK">&lt;link&gt;</ph>Search again<ph name="END_LINK">&lt;/link&gt;</ph>.
       </message>
       <message name="IDS_BLUETOOTH_ADAPTER_OFF" desc="The message to show when scanning cannot start because the bluetooth adapter is turned off.">
         Turn on Bluetooth in <ph name="BEGIN_LINK">&lt;link&gt;</ph>device settings<ph name="END_LINK">&lt;/link&gt;</ph> to allow pairing.
       </message>
       <message name="IDS_BLUETOOTH_ADAPTER_OFF_HELP" desc="The status message to show along with the message when the bluetooth adapter is turned off (to get Help).">
         <ph name="BEGIN_LINK">&lt;link&gt;</ph>Help<ph name="END_LINK">&lt;/link&gt;</ph>
       </message>
       <message name="IDS_BLUETOOTH_NEED_LOCATION_PERMISSION" desc="The message to show when scanning cannot start because Chrome needs the Location permission in order for Android to return any Bluetooth devices from a scan.">
-        Chrome needs location access to scan for devices. <ph name="BEGIN_LINK">&lt;link&gt;</ph>Update permissions<ph name="END_LINK">&lt;/link&gt;</ph>
+        Chrome needs location access to scan for devices. <ph name="BEGIN_LINK">&lt;permission_link&gt;</ph>Update permissions<ph name="END_LINK">&lt;/permission_link&gt;</ph>
+      </message>
+      <message name="IDS_BLUETOOTH_NEED_LOCATION_SERVICES_ON" desc="The message to show when scanning cannot start because Android location services are off, but they must be turned on for Android to return any Bluetooth devices from a scan.">

[scheib, 2016/06/03 20:48:29]

I left string thoughts on
https://bugs.chromium.org/p/chromium/issues/detail?id=545867

[Jeffrey Yasskin, 2016/06/06 16:16:56]

I've updated the strings to roughly Rebecca's suggestions, and will wait for her
to approve them on the bug.

+        Chrome needs location services to be turned on to scan for devices. <ph name="BEGIN_LINK">&lt;services_link&gt;</ph>Turn them on<ph name="END_LINK">&lt;/services_link&gt;</ph>
+      </message>
+      <message name="IDS_BLUETOOTH_NEED_LOCATION_PERMISSION_AND_SERVICES_ON" desc="The message to show when scanning cannot start because Chrome doesn't have the Location permission and the device's location services are turned off, and both must be enabled in order for Android to return any Bluetooth devices from a scan.">
+        Chrome needs location access to scan for devices. <ph name="BEGIN_LINK1">&lt;permission_link&gt;</ph>Update permissions<ph name="END_LINK1">&lt;/permission_link&gt;</ph>  <ph name="BEGIN_LINK2">&lt;services_link&gt;</ph>Turn on location services<ph name="END_LINK2">&lt;/services_link&gt;</ph>
       </message>
       <message name="IDS_BLUETOOTH_NEED_LOCATION_PERMISSION_HELP" desc="The status message to get more information about why Chrome needs the Location permission in order to scan for Bluetooth devices.">
         <ph name="BEGIN_LINK">&lt;link&gt;</ph>Help<ph name="END_LINK">&lt;/link&gt;</ph>
       </message>
 
       <!-- Sync error strings -->
       <message name="IDS_SYNC_ERROR_GENERIC" desc="Sync error string for generic error. [CHAR-LIMIT=80]">
         Sync error
       </message>
       <message name="IDS_SYNC_ERROR_GA" desc="Sync error string for when the needs to update the sign-in details [CHAR-LIMIT=80]">
@@ skipping 1230 matching lines @@
       <!-- Migration strings -->
       <message name="IDS_TAB_SWITCHER_CALLOUT_HEADER" desc="Header for the Tab Switcher callout.">
         Quickly switch tabs
       </message>
       <message name="IDS_TAB_SWITCHER_CALLOUT_BODY" desc="Indicates that clicking the tab switcher button gives you quick access to your tabs.">
         Tap this button for quick access to your tabs.
       </message>
     </messages>
   </release>
 </grit>