The latest version of Chrome (46.0.2490.86) appears to have changed behaviour again. This time, AutoFill has nothing to do with autocomplete
or readonly
or other workarounds suggested here (and on these bug reports https://code.google.com/p/chromium/issues/detail?id=468153, https://bugs.chromium.org/p/chromium/issues/detail?id=587466)
Rather, AutoFill now looks at the label next to the input box and generates an AutoFill based on that (as well as the id and name). A big clue is how AutoFill can actually fill multiple fields at once (e.g. Street, Suburb and State). It appears to be using several techniques (label, name, id) to discern the spatial relationship between fields.
So a workaround is to insert junk text into the label inside a hidden span...
S<span style="display:none">_</span>uburb:
...and also obfuscate/remove the id and name. This was the only thing that prevented Suburb AutoFill for me.