Fix "unused variable" warnings.

extensions/browser/api/hid/hid_api.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_API_HID_HID_API_H_
 #define EXTENSIONS_BROWSER_API_HID_HID_API_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 47 matching lines @@
 
  private:
   ~HidGetUserSelectedDevicesFunction() override;
 
   // ExtensionFunction:
   ResponseAction Run() override;
 
   void OnDevicesChosen(
       const std::vector<scoped_refptr<device::HidDeviceInfo>>& devices);
 
-  HidDeviceManager* device_manager_;
   std::unique_ptr<DevicePermissionsPrompt> prompt_;
 
   DISALLOW_COPY_AND_ASSIGN(HidGetUserSelectedDevicesFunction);
 };
 
 class HidConnectFunction : public UIThreadExtensionFunction {
  public:
   DECLARE_EXTENSION_FUNCTION("hid.connect", HID_CONNECT);
 
   HidConnectFunction();
@@ skipping 128 matching lines @@
   void OnFinished(bool success);
 
   std::unique_ptr<api::hid::SendFeatureReport::Params> parameters_;
 
   DISALLOW_COPY_AND_ASSIGN(HidSendFeatureReportFunction);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_HID_HID_API_H_