Support USB device hotplug on Android.

device/usb/usb_device_android.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 DEVICE_USB_USB_DEVICE_ANDROID_H_
 #define DEVICE_USB_USB_DEVICE_ANDROID_H_
 
 #include "base/android/scoped_java_ref.h"
 #include "device/usb/usb_device.h"
 
 namespace device {
 
 class UsbDeviceAndroid : public UsbDevice {
  public:
   // Register C++ methods exposed to Java using JNI.
   static bool RegisterJNI(JNIEnv* env);
 
   static scoped_refptr<UsbDeviceAndroid> Create(
       JNIEnv* env,
       const base::android::JavaRef<jobject>& usb_device);
 
   // UsbDevice:
   void Open(const OpenCallback& callback) override;
   const UsbConfigDescriptor* GetActiveConfiguration() const override;
 
+  jint device_id() const { return device_id_; }
+
  private:
   UsbDeviceAndroid(JNIEnv* env,
                    uint16_t usb_version,
                    uint8_t device_class,
                    uint8_t device_subclass,
                    uint8_t device_protocol,
                    uint16_t vendor_id,
                    uint16_t product_id,
                    uint16_t device_version,
                    const base::string16& manufacturer_string,
                    const base::string16& product_string,
                    const base::string16& serial_number,
                    const base::android::JavaRef<jobject>& wrapper);
   ~UsbDeviceAndroid() override;
 
+  const jint device_id_;
+
   // Java object org.chromium.device.usb.ChromeUsbDevice.
   base::android::ScopedJavaGlobalRef<jobject> j_object_;
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_DEVICE_ANDROID_H_