arc: Implement Read and GetFileSize for ARC content file system

chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_CONTENT_FILE_SYSTEM_URL_UTIL_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_CONTENT_FILE_SYSTEM_URL_UTIL_H_
 
 #include "base/files/file_path.h"
 #include "url/gurl.h"
 
+namespace storage {
+class FileSystemURL;
+}
+
 namespace arc {
 
 // The name of the ARC content file system mount point.
 extern const char kMountPointName[];
 
 // The path of the ARC content file system mount point.
 extern const base::FilePath::CharType kMountPointPath[];
 
 // Converts a URL which can be used within the ARC container to an externalfile:
 // URL which can be used by Chrome.
 GURL ArcUrlToExternalFileUrl(const GURL& arc_url);
 
 // Converts an externalfile: URL to a URL which can be used within the ARC
 // container. If the given URL cannot be converted to an ARC URL, returns an
 // empty GURL.
 GURL ExternalFileUrlToArcUrl(const GURL& external_file_url);
 
+// Converts a FileSystemURL to a URL which can be used within the ARC container.
+GURL FileSystemUrlToArcUrl(const storage::FileSystemURL& url);
+
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_CONTENT_FILE_SYSTEM_URL_UTIL_H_