Support overriding fields in DDC

[mit-mit]

This is the DDC part of meta-issue #28117.
#27385 tracks supporting this via an @virtual modifier, however the 1.50 design does not require such a modifier on field overrides.

[jmesserly]

DDC supports this once the fix lands for #27385

it's based on Analyzer marking fields as isVirtual, DDC itself doesn't use @virtual

so any change to Analyzer will be picked up by DDC (see #28120), it is unclear to me what the affect will be on internal code performance/size. Someone should try it out once fix lands for #27385

[vsmenon]

We need to ensure this does not regress large app experience for our customers before we drop the modifier.

[mit-mit]

We need to ensure this does not regress large app experience for our customers before we drop the modifier.

@vsmenon what is the plan and schedule for that testing?

[vsmenon]

Once Jen's change lands internally, we will test the effect of marking all fields isVirtual/@virtual on code size and load time.

[mit-mit]

The fix looks to be in 1.22.0-dev.2.0, let me figure out when that can be rolled.

[kasperl]

Who owns this, @vsmenon / @leafpetersen? This is blocking the 1.23 release so we need an owner now.

[kasperl]

This is the issue we talked about yesterday, @dgrove. It doesn't appear to have had an assignee ever.

[leafpetersen]

There was a request to use this bug for updates. I have an AR to take measurements of the code size and latency cost for DDC of turning this on by default. I've been pulled back into the internal roll today and likely will be tomorrow as well, so no progress to report.

[kasperl]

Proposed CL here: https://codereview.chromium.org/2691433004/.

[kasperl]

Blocked on #28809.

[vsmenon]

Our plan is to do #28801 to devirtualize most fields and treat the rest as virtual (i.e., what we were doing on @virtual but by default). #28801 will assume #28809.

[jmesserly]

https://codereview.chromium.org/2781443003/