Update USBConnectionEvent.idl to match the spec.

third_party/WebKit/Source/modules/webusb/USBConnectionEvent.cpp

 // 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.
 
 #include "modules/webusb/USBConnectionEvent.h"
 
 #include "modules/webusb/USBConnectionEventInit.h"
 #include "modules/webusb/USBDevice.h"
 
 namespace blink {
 
 USBConnectionEvent* USBConnectionEvent::create(const AtomicString& type, const USBConnectionEventInit& initializer)
 {
     return new USBConnectionEvent(type, initializer);
 }
 
 USBConnectionEvent* USBConnectionEvent::create(const AtomicString& type, USBDevice* device)
 {
     return new USBConnectionEvent(type, device);
 }
 
 USBConnectionEvent::USBConnectionEvent(const AtomicString& type, const USBConnectionEventInit& initializer)
     : Event(type, initializer)
-    , m_device(nullptr)
+    , m_device(initializer.device())
 {
-    if (initializer.hasDevice())
-        m_device = initializer.device();
 }
 
 USBConnectionEvent::USBConnectionEvent(const AtomicString& type, USBDevice* device)
     : Event(type, false, false)
     , m_device(device)
 {
 }
 
 DEFINE_TRACE(USBConnectionEvent)
 {
     visitor->trace(m_device);
     Event::trace(visitor);
 }
 
 } // namespace blink