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

content/renderer/bluetooth/bluetooth_dispatcher.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_CHILD_BLUETOOTH_BLUETOOTH_DISPATCHER_H_
 #define CONTENT_CHILD_BLUETOOTH_BLUETOOTH_DISPATCHER_H_
 
 #include "base/id_map.h"
 #include "base/memory/ref_counted.h"
 #include "content/child/worker_task_runner.h"
@@ skipping 32 matching lines @@
   // Gets or Creates a BluetoothDispatcher for the current thread.
   // |thread_safe_sender| is required when constructing a BluetoothDispatcher.
   static BluetoothDispatcher* GetOrCreateThreadSpecificInstance(
       ThreadSafeSender* thread_safe_sender);
 
   // IPC Send and Receiving interface, see IPC::Sender and IPC::Listener.
   bool Send(IPC::Message* msg);
   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);
   void getPrimaryService(
       const blink::WebString& device_instance_id,
       const blink::WebString& service_uuid,
       blink::WebBluetoothGetPrimaryServiceCallbacks* callbacks);
 
   void getCharacteristic(
       const blink::WebString& service_instance_id,
@@ skipping 70 matching lines @@
       pending_read_value_requests_;
   IDMap<blink::WebBluetoothWriteValueCallbacks, IDMapOwnPointer>
       pending_write_value_requests_;
 
   DISALLOW_COPY_AND_ASSIGN(BluetoothDispatcher);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_BLUETOOTH_BLUETOOTH_DISPATCHER_H_