Prevent Chrome autofilling phone numbers into 'Other amount' fields

On our website Chrome decided that the 'Other Amount' field was a phone number, and cheerily autofilled it. This meant that people who intended to donate 2-figure sums ended up donating 4-figure sums. Entertaining video here: https://drive.google.com/file/d/0B5j9ZbkpU3FXMTE5VUJXX0xVSVU/view

You can turn off autocomplete for individual fields. We did it with javascript:

$('.other_amount-content input').attr("autocomplete", "off");

I'm not sure of the best way to fix this in core, though.