[Blink-FileAPI] Add the notification of update observer.

storage/browser/fileapi/file_system_operation_runner.cc

Index: storage/browser/fileapi/file_system_operation_runner.cc
diff --git a/storage/browser/fileapi/file_system_operation_runner.cc b/storage/browser/fileapi/file_system_operation_runner.cc
index 58ccb94d67cd4e90c8304a9cbeb48fa88b20da34..097fd55da1515852da88d8cbe7078b9a9fc53f8f 100644
--- a/storage/browser/fileapi/file_system_operation_runner.cc
+++ b/storage/browser/fileapi/file_system_operation_runner.cc
@@ -402,6 +402,7 @@ OperationID FileSystemOperationRunner::CopyInForeignFile(
     DidFinish(handle, callback, error);
     return handle.id;
   }
+  PrepareForWrite(handle.id, dest_url);
   operation->CopyInForeignFile(
       src_local_disk_path, dest_url,
       base::Bind(&FileSystemOperationRunner::DidFinish, AsWeakPtr(),