Support USB device hotplug on Android.

device/usb/usb_device_android.h

Index: device/usb/usb_device_android.h
diff --git a/device/usb/usb_device_android.h b/device/usb/usb_device_android.h
index 9355837f07ef5db0dbc7c381310a7f70290d4183..263b4dbd5f022f642165a997e8690956aa36d7d7 100644
--- a/device/usb/usb_device_android.h
+++ b/device/usb/usb_device_android.h
@@ -23,6 +23,8 @@ class UsbDeviceAndroid : public 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,
@@ -38,6 +40,8 @@ class UsbDeviceAndroid : public UsbDevice {
                    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_;
 };