There is some case where we throw StorageException after failing to
submit (usually happens in large topics with many changes). In such a
case, we don't want to report a StorageException to ensure that the user
knows what happens.
The UI will hide the details of a StorageException but should show the
details of InternalServerWithUserMessageException (since we configured
it to show the message in ExceptionHookImpl).
Change-Id: I9601f321cb778de18727a3843376114f81ff05c7
5fdaa63ec0