This is a Chrome plugin handling it instead of having Chrome download it.
Settings>Advanced>Content Settings>Disable Individual Plugins...
And then disable or modify whichever one is handling m3u
files.
If it still doesn't work, there may be a silver shield icon displayed up in on the right side of the address/search bar, next to the bookmark star:
I encountered that when running on my self-signed SSL home server and had to enable the loading of the "unsafe script".