There does not seem to be any published specification of -webkit-text-size-adjust, but there is e.g. an informal description, which says that it works in Safari on iPhone.
According to CSS Mobile Text Size Adjustment Module Level (Editor’s Draft), auto is the initial value, so -webkit-text-size-adjust:none would have an effect only when it overrides a setting that sets the property to a different value. Presumably -webkit-text-size-adjust works mostly the same way as the planned text-size-adjust property.
