UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Safari/537.36

Steps to reproduce the problem:
1. Open Device Mode in Developer Tools
2. Click the 3 vertical dots in the top right and 'Capture screenshot'
3. Screenshot downloads in PNG format with no option to choose the format. 

What is the expected behavior?
The user should be able to specify whether images should be saved as PNGs (the default today) or JPGs. 

What went wrong?
The screenshot downloaded as a PNG with no option to download it as a JPG. Most screenshot extensions allow the user to choose the file type they want to download. 

Did this work before? N/A 

Chrome version: 62.0.3202.94  Channel: stable
OS Version: OS X 10.12.6
Flash Version: