GitLab

During destruction, pdfium may call back into the instance and access members.
It would be better if this didn't happen but it isn't strictly wrong and may
be necessary as it appears pdfium can run scripts at shutdown.

BUG=485855
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1144923002

Cr-Commit-Position: refs/heads/master@{#330684}