UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Safari/537.36

Steps to reproduce the problem:
Please see https://bugs.chromium.org/p/chromium/issues/detail?id=781133#c4 which was duped against an unrelated issue. The last comment contains repro steps. I didn't realize that replying to the duped bug would make it stay closed and can't seem to re-open it.

What is the expected behavior?

What went wrong?
See referenced bug - content is always assumed to be plain text.

Did this work before? No 

Chrome version: 64.0.3264.0  Channel: stable
OS Version: Puppeteer 0.13.0 (linux-515411)
Flash Version: