Reset webusb detector before browser client

components/webusb/webusb_detector.h

 // Copyright 2015 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 COMPONENTS_WEBUSB_WEBUSB_DETECTOR_H_
 #define COMPONENTS_WEBUSB_WEBUSB_DETECTOR_H_
 
 #include "base/scoped_observer.h"
 #include "device/usb/usb_service.h"
 
 namespace device {
 class UsbDevice;
 }
 
 namespace webusb {
 
 class UsbDevice;
 class WebUsbBrowserClient;
 
 class WebUsbDetector : public device::UsbService::Observer {
  public:
-  WebUsbDetector(WebUsbBrowserClient* webusb_browser_client);
+  explicit WebUsbDetector(WebUsbBrowserClient* webusb_browser_client);
 
   ~WebUsbDetector() override;
 
  private:
   // Initializes the WebUsbDetector.
   void Initialize();
 
   // UsbService::observer override:
   void OnDeviceAdded(scoped_refptr<device::UsbDevice> device) override;
 
   // UsbService::observer override:
   void OnDeviceRemoved(scoped_refptr<device::UsbDevice> device) override;
 
   WebUsbBrowserClient* webusb_browser_client_ = nullptr;
 
   ScopedObserver<device::UsbService, device::UsbService::Observer> observer_;
 
   DISALLOW_COPY_AND_ASSIGN(WebUsbDetector);
 };
 
 }  // namespace webusb
 
 #endif  // COMPONENTS_WEBUSB_WEBUSB_DETECTOR_H_