Use the task scheduler for blocking tasks in the USB service on Linux

device/usb/usb_service_linux.h

 // 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 <list>
 #include <memory>
 #include <unordered_map>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "device/usb/usb_service.h"
 
-namespace base {
-class SequencedTaskRunner;
-}
-
 namespace device {
 
 struct UsbDeviceDescriptor;
 class UsbDeviceLinux;
 
 class UsbServiceLinux : public UsbService {
  public:
-  explicit UsbServiceLinux(
-      scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_in);
+  UsbServiceLinux();
   ~UsbServiceLinux() override;
 
   // device::UsbService implementation
   void Shutdown() override;
   void GetDevices(const GetDevicesCallback& callback) override;
 
  private:
   using DeviceMap =
       std::unordered_map<std::string, scoped_refptr<UsbDeviceLinux>>;
 
@@ skipping 24 matching lines @@
 
   std::unique_ptr<FileThreadHelper> helper_;
   DeviceMap devices_by_path_;
 
   base::WeakPtrFactory<UsbServiceLinux> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UsbServiceLinux);
 };
 
 }  // namespace device