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..52cfdaea505b2ab4976362e07be7c8ace338b0f5 100644
--- a/webkit/browser/fileapi/file_system_backend.h
+++ b/webkit/browser/fileapi/file_system_backend.h
@@ -35,6 +35,9 @@ class FileSystemOperation;
 class FileSystemQuotaUtil;
 class WatcherManager;
 
+// Callback to take GURL.
+typedef base::Callback<void(const GURL& url)> URLCallback;
+
 // An interface for defining a file system backend.
 //
 // NOTE: when you implement a new FileSystemBackend for your own
@@ -157,6 +160,11 @@ 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 a redirect URL for browser tab. e.g. Google Drive URL for hosted
+  // documents. Returns empty URL if the entry does not have the redirect URL.
+  virtual void GetRedirectURLForBrowserTab(
+      const storage::FileSystemURL& url,
+      const storage::URLCallback& callback) = 0;
 };
 
 }  // namespace storage