Files.app: Enable externalfile: protocol for MTP volumes.

chrome/browser/chromeos/fileapi/external_file_url_util.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 CHROME_BROWSER_CHROMEOS_FILEAPI_EXTERNAL_FILE_URL_UTIL_H_
 #define CHROME_BROWSER_CHROMEOS_FILEAPI_EXTERNAL_FILE_URL_UTIL_H_
 
 class GURL;
 class Profile;
 
 namespace base {
 class FilePath;
 }
 
+namespace storage {
+class FileSystemURL;
+}
+
 namespace chromeos {
 
-// Returns the external file resource url formatted as "externalfile:<path>"
-GURL FilePathToExternalFileURL(const base::FilePath& path);
+// Obtains the external file url formatted as "externalfile:<path>" from file
+// path. Returns empty URL if the file system does not provide the external file
+// URL.
+GURL FileSystemURLToExternalFileURL(
+    const storage::FileSystemURL& file_system_url);
 
-// Converts a externalfile: URL back to a path that can be passed to FileSystem.
-base::FilePath ExternalFileURLToFilePath(const GURL& url);
+// Converts a externalfile: URL back to a virtual path of FileSystemURL.
+base::FilePath ExternalFileURLToVirtualPath(Profile* profile, const GURL& url);
 
 // Overwrites |url| with an external file URL when appropriate.
 void MaybeSetExternalFileURL(Profile* profile,
                              const base::FilePath& path,
                              GURL* url);
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILEAPI_EXTERNAL_FILE_URL_UTIL_H_