Put the RenderFrame's ID into a per-frame WebBluetooth, and plumb that back to the browser.

content/renderer/bluetooth/bluetooth_dispatcher.h

Index: content/renderer/bluetooth/bluetooth_dispatcher.h
diff --git a/content/renderer/bluetooth/bluetooth_dispatcher.h b/content/renderer/bluetooth/bluetooth_dispatcher.h
index 97e43cd52cbc8d0d8ae8437f26017fb592380a80..1a704a71824c89aa331fb5e5e8e28132564a3abc 100644
--- a/content/renderer/bluetooth/bluetooth_dispatcher.h
+++ b/content/renderer/bluetooth/bluetooth_dispatcher.h
@@ -50,7 +50,8 @@ class BluetoothDispatcher : public WorkerTaskRunner::Observer {
   void OnMessageReceived(const IPC::Message& msg);
 
   // Corresponding to WebBluetoothImpl methods.
-  void requestDevice(const blink::WebRequestDeviceOptions& options,
+  void requestDevice(int frame_routing_id,
+                     const blink::WebRequestDeviceOptions& options,
                      blink::WebBluetoothRequestDeviceCallbacks* callbacks);
   void connectGATT(const blink::WebString& device_instance_id,
                    blink::WebBluetoothConnectGATTCallbacks* callbacks);