Delay WebUSB initialization until after browser startup.

chrome/browser/usb/web_usb_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 CHROME_BROWSER_USB_WEB_USB_DETECTOR_H_
 #define CHROME_BROWSER_USB_WEB_USB_DETECTOR_H_
 
 #include "base/macros.h"
 #include "base/scoped_observer.h"
 #include "device/usb/usb_service.h"
 
 namespace device {
 class UsbDevice;
 }
 
 class UsbDevice;
 
 class WebUsbDetector : public device::UsbService::Observer {
  public:
   WebUsbDetector();
   ~WebUsbDetector() override;
 
- private:
   // Initializes the WebUsbDetector.
   void Initialize();
 
+ private:
   // device::UsbService::observer:
   void OnDeviceAdded(scoped_refptr<device::UsbDevice> device) override;
   void OnDeviceRemoved(scoped_refptr<device::UsbDevice> device) override;
 
   ScopedObserver<device::UsbService, device::UsbService::Observer> observer_;
 
   DISALLOW_COPY_AND_ASSIGN(WebUsbDetector);
 };
 
 #endif  // CHROME_BROWSER_USB_WEB_USB_DETECTOR_H_