Remove MTP support on Linux.

chrome/browser/media_galleries/fileapi/media_file_system_backend.h

 // Copyright (c) 2013 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 CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_MEDIA_FILE_SYSTEM_BACKEND_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_MEDIA_FILE_SYSTEM_BACKEND_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 13 matching lines @@
 }
 
 namespace storage {
 class FileSystemURL;
 }
 
 namespace net {
 class URLRequest;
 }
 
+class DeviceMediaAsyncFileUtil;
 class MediaPathFilter;
-class DeviceMediaAsyncFileUtil;
 
 class MediaFileSystemBackend : public storage::FileSystemBackend {
  public:
   static const char kMediaTaskRunnerName[];
 
   MediaFileSystemBackend(
       const base::FilePath& profile_path,
       base::SequencedTaskRunner* media_task_runner);
   ~MediaFileSystemBackend() override;
 
@@ skipping 57 matching lines @@
   // Store the profile path. We need this to create temporary snapshot files.
   const base::FilePath profile_path_;
 
   scoped_refptr<base::SequencedTaskRunner> media_task_runner_;
 
   std::unique_ptr<MediaPathFilter> media_path_filter_;
   std::unique_ptr<storage::CopyOrMoveFileValidatorFactory>
       media_copy_or_move_file_validator_factory_;
 
   std::unique_ptr<storage::AsyncFileUtil> native_media_file_util_;
+
+#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_CHROMEOS)
   std::unique_ptr<DeviceMediaAsyncFileUtil> device_media_async_file_util_;
+#endif
+
 #if defined(OS_WIN) || defined(OS_MACOSX)
   std::unique_ptr<storage::AsyncFileUtil> picasa_file_util_;
   std::unique_ptr<storage::AsyncFileUtil> itunes_file_util_;
 
   // Used for usage UMA tracking.
   bool picasa_file_util_used_;
   bool itunes_file_util_used_;
-#endif  // defined(OS_WIN) || defined(OS_MACOSX)
+#endif
 
   DISALLOW_COPY_AND_ASSIGN(MediaFileSystemBackend);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_MEDIA_FILE_SYSTEM_BACKEND_H_