Enable WebUSB device detection when using the new Windows USB backend.

chrome/browser/usb/web_usb_detector.cc

 // 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 "chrome/browser/usb/web_usb_detector.h"
 
 #include <utility>
 
+#include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/net/referrer.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/scoped_tabbed_browser_displayer.h"
 #include "chrome/grit/generated_resources.h"
 #include "chrome/grit/theme_resources.h"
 #include "content/public/common/origin_util.h"
 #include "device/base/device_client.h"
+#include "device/base/features.h"
 #include "device/usb/usb_device.h"
 #include "device/usb/usb_ids.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/page_transition_types.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/base/window_open_disposition.h"
 #include "ui/gfx/image/image.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/notification.h"
 #include "ui/message_center/notification_delegate.h"
@@ skipping 81 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(WebUsbNotificationDelegate);
 };
 
 }  // namespace
 
 WebUsbDetector::WebUsbDetector() : observer_(this) {}
 
 WebUsbDetector::~WebUsbDetector() {}
 
 void WebUsbDetector::Initialize() {
-// Disabled on Windows due to jank and hangs caused by enumerating devices.
-// https://crbug.com/656702
-#if !defined(OS_WIN)
+#if defined(OS_WIN)
+  // The WebUSB device detector is disabled on Windows due to jank and hangs
+  // caused by enumerating devices. The new USB backend is designed to resolve
+  // these issues so enable it for testing. https://crbug.com/656702
+  if (!base::FeatureList::IsEnabled(device::kNewUsbBackend))
+    return;
+#endif  // defined(OS_WIN)
+
   SCOPED_UMA_HISTOGRAM_TIMER("WebUsb.DetectorInitialization");
   device::UsbService* usb_service =
       device::DeviceClient::Get()->GetUsbService();
   if (!usb_service)
     return;
 
   observer_.Add(usb_service);
-#endif
 }
 
 void WebUsbDetector::OnDeviceAdded(scoped_refptr<device::UsbDevice> device) {
   const base::string16& product_name = device->product_string();
   if (product_name.empty()) {
     return;
   }
 
   const GURL& landing_page = device->webusb_landing_page();
   if (!landing_page.is_valid() || !content::IsOriginSecure(landing_page)) {
@@ skipping 25 matching lines @@
 }
 
 void WebUsbDetector::OnDeviceRemoved(scoped_refptr<device::UsbDevice> device) {
   std::string notification_id = device->guid();
   message_center::MessageCenter* message_center =
       message_center::MessageCenter::Get();
   if (message_center->FindVisibleNotificationById(notification_id)) {
     message_center->RemoveNotification(notification_id, false /* by_user */);
   }
 }