We weren't deleting them correctly - the intention was to delete
them when an instance is finalized; the code was deleting them
only for the last instance in a chain of instances.

Bug: 
Change-Id: I177a64ac9f10a4993927d9654c032cb3f22eca51
Reviewed-on: https://chromium-review.googlesource.com/651238Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47841}