Add GetURLForBrowserTab method to the external file system backend.

webkit/browser/fileapi/file_system_backend.h

 // 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.
 
 #ifndef WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_
 #define WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 139 matching lines @@
   virtual void GrantFileAccessToExtension(
       const std::string& extension_id,
       const base::FilePath& virtual_path) = 0;
   // Revokes file access from extension identified with |extension_id|.
   virtual void RevokeAccessForExtension(
         const std::string& extension_id) = 0;
   // Gets virtual path by known filesystem path. Returns false when filesystem
   // path is not exposed by this provider.
   virtual bool GetVirtualPath(const base::FilePath& file_system_path,
                               base::FilePath* virtual_path) = 0;
+  // Gets an alternative URL for browser tab. e.g. Google Drive URL for hosted

[mtomasz, 2014/09/03 09:44:42]

nit: "alternative" sounds strange. It means that either is fine (you have an
alternative). How about:
1. alternative -> fallback (since the browser fallbacks to it if the file
contents are not available locally)
2. alternative -> content (since it's an URL for contents)
3. alternative -> redirect (since it's used for redirection)?

WDYT?

[hirono, 2014/09/03 13:02:45]

I chose "redirect" URL.

+  // documents. Returns empty URL if the entry does not have an alternatvie URL.
+  virtual void GetURLForBrowserTab(
+      const storage::FileSystemURL& url,
+      const base::Callback<void(const GURL& url)>& callback) = 0;

[mtomasz, 2014/09/03 09:44:42]

nit: How about typedefing this callback like in #46?

[hirono, 2014/09/03 13:02:45]

Done.

 };
 
 }  // namespace storage
 
 #endif  // WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_