UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36

Steps to reproduce the problem:
1. Open Chrome 59/60
2. Go to directory with index.html, run SimpleHTTPServer or something similar (for cors reasons)
3. Open console, run test().
4. Observe times.
5. Repeat on Chrome 58

What is the expected behavior?
Times should be similar or better on Chrome 59.

What went wrong?
Chrome 59 is significantly slower loading a stack of 256 images.

Did this work before? Yes 58

Does this work in other browsers? N/A

Chrome version: 60.0.3112.90  Channel: stable
OS Version: OS X 10.11.6
Flash Version: Shockwave Flash 26.0 r0

If you change the call of downloadStackDecode to downloadStack, you will see that times are consistent when loading the images without decoding them.
 

Deleted: index.html 36 bytes

index.html 36 bytes View Download

Deleted: script.js 1.1 KB

script.js 1.1 KB View Download