Add a feature flag for the new Windows USB backend.

device/usb/usb_service_linux.cc

 // Copyright 2016 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 "device/usb/usb_service_linux.h"
 
 #include <stdint.h>
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_restrictions.h"
-#include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "components/device_event_log/device_event_log.h"
 #include "device/base/device_monitor_linux.h"
 #include "device/usb/usb_device_handle.h"
 #include "device/usb/usb_device_linux.h"
 #include "device/usb/webusb_descriptors.h"
 
 namespace device {
 
 namespace {
@@ skipping 142 matching lines @@
   const char* device_path = udev_device_get_devnode(device);
   if (device_path) {
     task_runner_->PostTask(
         FROM_HERE, base::Bind(&UsbServiceLinux::OnDeviceRemoved, service_,
                               std::string(device_path)));
   }
 }
 
 UsbServiceLinux::UsbServiceLinux(
     scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_in)
-    : UsbService(base::ThreadTaskRunnerHandle::Get(),
-                 std::move(blocking_task_runner_in)),
-      weak_factory_(this) {
+    : UsbService(std::move(blocking_task_runner_in)), weak_factory_(this) {
   helper_ = base::MakeUnique<FileThreadHelper>(weak_factory_.GetWeakPtr(),
                                                task_runner());
   blocking_task_runner()->PostTask(
       FROM_HERE,
       base::Bind(&FileThreadHelper::Start, base::Unretained(helper_.get())));
 }
 
 UsbServiceLinux::~UsbServiceLinux() {
   DCHECK(!helper_);
 }
@@ skipping 117 matching lines @@
     result.reserve(devices().size());
     for (const auto& map_entry : devices())
       result.push_back(map_entry.second);
     for (const auto& callback : enumeration_callbacks_)
       callback.Run(result);
     enumeration_callbacks_.clear();
   }
 }
 
 }  // namespace device