Use the Mojo StubBindings interface correctly in WebUSB LayoutTests.

third_party/WebKit/Source/modules/webusb/USB.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/USB.h"
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/Document.h"
@@ skipping 144 matching lines @@
     m_deviceManagerRequests.remove(resolver);
 }
 
 void USB::onGetPermission(ScriptPromiseResolver* resolver, usb::DeviceInfoPtr deviceInfo)
 {
     auto requestEntry = m_chooserServiceRequests.find(resolver);
     if (requestEntry == m_chooserServiceRequests.end())
         return;
     m_chooserServiceRequests.remove(requestEntry);
 
+    if (!m_deviceManager) {
+        resolver->reject(DOMException::create(NotFoundError, kNoServiceError));
+        return;
+    }
+
     if (deviceInfo) {
         usb::DevicePtr device;
         m_deviceManager->GetDevice(deviceInfo->guid, mojo::GetProxy(&device));
         resolver->resolve(USBDevice::create(std::move(deviceInfo), std::move(device), resolver->getExecutionContext()));
     } else {
         resolver->reject(DOMException::create(NotFoundError, "No device selected."));
     }
 }
 
 void USB::onDeviceChanges(usb::DeviceChangeNotificationPtr notification)
@@ skipping 26 matching lines @@
 
 DEFINE_TRACE(USB)
 {
     EventTargetWithInlineData::trace(visitor);
     ContextLifecycleObserver::trace(visitor);
     visitor->trace(m_deviceManagerRequests);
     visitor->trace(m_chooserServiceRequests);
 }
 
 } // namespace blink