Plumb file system name down from MediaFileSystemRegistry.

chrome/common/extensions/extension_constants.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/common/extensions/extension_constants.h"
 #include "chrome/common/extensions/extension_manifest_constants.h"
 
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 122 matching lines @@
 const char kChromeVoxDirectoryName[] = "access_chromevox";
 #endif
 
 const char kAppStateNotInstalled[] = "not_installed";
 const char kAppStateInstalled[] = "installed";
 const char kAppStateDisabled[] = "disabled";
 const char kAppStateRunning[] = "running";
 const char kAppStateCannotRun[] = "cannot_run";
 const char kAppStateReadyToRun[] = "ready_to_run";
 
+const char kMediaFileSystemPathPart[] = "_";
+
 const char kAppNotificationsIncognitoError[] =
     "This API is not accessible by 'split' mode "
     "extensions in incognito windows.";
 
 }  // namespace extension_misc