Add GetURLForBrowserTab method to the external file system backend.

webkit/browser/fileapi/file_system_backend.h

Index: webkit/browser/fileapi/file_system_backend.h
diff --git a/webkit/browser/fileapi/file_system_backend.h b/webkit/browser/fileapi/file_system_backend.h
index b71c8cab06d7fce114b06a3ade098dff8084f165..1093e0fd4aa561a0b181f6c341147b16c2a725c9 100644
--- a/webkit/browser/fileapi/file_system_backend.h
+++ b/webkit/browser/fileapi/file_system_backend.h
@@ -157,6 +157,11 @@ class ExternalFileSystemBackend : public FileSystemBackend {
   // 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