Use the Mojo StubBindings interface correctly in WebUSB LayoutTests.

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

Index: third_party/WebKit/Source/modules/webusb/USB.cpp
diff --git a/third_party/WebKit/Source/modules/webusb/USB.cpp b/third_party/WebKit/Source/modules/webusb/USB.cpp
index c0d31969cb0716322bacd1c8ffa8e9f4a99d8cef..0d48fefee1d5251fa701692982fb2c92aaa390c3 100644
--- a/third_party/WebKit/Source/modules/webusb/USB.cpp
+++ b/third_party/WebKit/Source/modules/webusb/USB.cpp
@@ -162,6 +162,11 @@ void USB::onGetPermission(ScriptPromiseResolver* resolver, usb::DeviceInfoPtr de
         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));