Add webusb notification UI code

components/webusb/webusb_detector.h

Index: components/webusb/webusb_detector.h
diff --git a/components/webusb/webusb_detector.h b/components/webusb/webusb_detector.h
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index 0000000000000000000000000000000000000000..534373970f07bcb37cdd775ceaf4e0ff7ab1b125
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+++ b/components/webusb/webusb_detector.h
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+// 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"
+
+template <typename T>
+struct DefaultSingletonTraits;
+
+namespace device {
+class UsbDevice;
+}
+
+namespace webusb {
+
+class UsbDevice;
+
+class WebUsbDetector : public device::UsbService::Observer {
+ public:
+  static WebUsbDetector* GetInstance();
+
+  ~WebUsbDetector() override;
+
+ private:
+  friend struct DefaultSingletonTraits<WebUsbDetector>;
+  WebUsbDetector();
+
+  // UsbService::observer override:
+  void OnDeviceAdded(scoped_refptr<device::UsbDevice> device) override;
+
+  // UsbService::observer override:
+  void OnDeviceRemoved(scoped_refptr<device::UsbDevice> device) override;
+
+  // Initializes the WebUsbDetector.
+  void Initialize();
+
+  ScopedObserver<device::UsbService, device::UsbService::Observer> observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebUsbDetector);
+};
+
+}  // namespace webusb
+
+#endif  // COMPONENTS_WEBUSB_WEBUSB_DETECTOR_H_