UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.117 Safari/537.36

Steps to reproduce the problem:
1. Open http://pdftron.s3.amazonaws.com/downloads/webviewer/test/samples/basic/index.html?doctype=pdf
2. Select different documents from the dropdown at the top and confirm that they load without issue.
3. Press the Toggle Visibility button to hide the viewer. Then press it again to show the viewer.
4. Select another document from the dropdown and the NaCl module will crash.

What is the expected behavior?
After toggling the visibility new documents can continue to be loaded and there is no crash.

What went wrong?
It's unclear. I installed Chrome 64 and confirmed that it was working without issue and Chrome 65 is when it started happening.

Did this work before? Yes Chrome 64

Does this work in other browsers? Yes

Chrome version: 66.0.3359.117  Channel: stable
OS Version: 10.0
Flash Version: