I know there are certain tricks to disable zooming when making a web page, but how do I disable zoom on focus on my device?
I have Paranoid Android and the Xposed Framework, so, I know anything is possible.
Unfortunately, the answer is that you can't.
That's confirmed pretty conclusively by this bug report/feature request thread in the Chrome development forum. The thread goes all the way back to last March, and posts as recent as a week and a half ago indicate that a means of disabling this behavior has not been implemented.
Sadly, recent indications are that the dev team is disinclined to implement such a setting in the future. Despite input from several people providing examples of how this feature can be an impediment, and requesting a setting to disable it, this response from a developer says that they avoid adding new settings, and they'd rather work on making it "less annoying":
#12: I haven't really noticed it zooming in on mobile sites. When it does, we can consider that a bug, but I don't think a modal ban is the right approach. I'd rather continuing tuning the policy so that it doesn't trigger when inappropriate. Note also that the same code deals with animating the scroll position around when the on-screen-keyboard would cover the form field. That behavior definitely desirable to preserve even on mobile sites.
#13: We generally try to avoid adding settings in Chrome; we'd rather tune this so it's less annoying for all users, not just the ones who discover the setting. We already made a few improvements to make this trigger less frequently since the bug was originally filed; we might benefit from loosening it further to tolerate further zoom levels.
<rant>I think that's a terrible answer. What he's essentially saying is that they'd rather make Procrustean decisions for all users, based on the developers' subjective judgment and applying only to situations that they anticipate or have already been brought to their attention, than allow users to decide for themselves whether they want this behavior or not. And the argument that they'd "rather tune this so it's less annoying for all users, not just the ones who discover the setting" is a logical fallacy: there's absolutely no reason whatsoever why the two are mutually exclusive.
This "KISS principle", one-size-fits-all Cupertino mentality is why I hardly ever touch Chrome on any non-Google OS, and even on Android I use Firefox half the time. </rant>
But the bottom line is that it sounds like it's not possible and it's not going to be.
Or, the sarcastic but correct answer is: you can disable this behavior by using a browser other than Chrome, at least for any sites where you don't want automatic zooming on focus.
I figured it out for FireFox users:
This is especially beneficial to navigating websites in desktop mode, without that nasty input zoom.
My solution that may help was to install am app called Windows Manipulator on my android phone then set the DPI significantly lower. This gives me enough screen real estate (albeit with significantly smaller font). This seems to keep Chrome from zooming on focus as often. I also switched to Flashfox Pro browser which does not zoom on focus frequently. These 2 fixes combined have eliminated my complaints. Hope this helps someone.