[CrOS Tether] Sort Tether network lists.

chromeos/components/tether/host_scan_device_prioritizer.h

 // Copyright 2017 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.
 
 #ifndef CHROMEOS_COMPONENTS_TETHER_HOST_SCAN_DEVICE_PRIORITIZER_H_
 #define CHROMEOS_COMPONENTS_TETHER_HOST_SCAN_DEVICE_PRIORITIZER_H_
 
 #include "base/macros.h"
 #include "components/cryptauth/remote_device.h"
 
 namespace chromeos {
 
 namespace tether {
 
-class TetherHostResponseRecorder;
-
 // Prioritizes the order of devices when performing a host scan. To optimize for
 // the most common tethering operations, this class uses the following rules:
 //   * The device which has most recently sent a successful
 //     ConnectTetheringResponse is always at the front of the queue.
 //   * Devices which have most recently sent a successful
 //     TetherAvailabilityResponse are next in the order, as long as they do not
 //     violate the first rule.
 //   * All other devices are left in the order they are passed.
 class HostScanDevicePrioritizer {
  public:
-  HostScanDevicePrioritizer(
-      TetherHostResponseRecorder* tether_host_response_recorder);
-  virtual ~HostScanDevicePrioritizer();
+  HostScanDevicePrioritizer() {}
+  virtual ~HostScanDevicePrioritizer() {}
 
   // Prioritizes |remote_devices| using the rules described above.
   virtual void SortByHostScanOrder(
-      std::vector<cryptauth::RemoteDevice>* remote_devices) const;
+      std::vector<cryptauth::RemoteDevice>* remote_devices) const = 0;
 
  private:
-  TetherHostResponseRecorder* tether_host_response_recorder_;
-
   DISALLOW_COPY_AND_ASSIGN(HostScanDevicePrioritizer);
 };
 
 }  // namespace tether
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_COMPONENTS_TETHER_HOST_SCAN_DEVICE_PRIORITIZER_H_