Enable MessageLoop implementation by default

[gaearon]

This disables the RAF scheduler impl in favor of the MessageLoop one, which we've found better utilizes CPU. Unlike #16271, this keeps the RAF implementation for now just in case, but it's only in one specially marked test.

This matches what we already rolled out in www, except the rAF-specific flags (they're true on www but they're dead code in the rAF path anyway — and I didn't want to adjust the test for them).

My previous PR includes most of the extra test coverage for ML scheduler which I picked up from Andrew's earlier PR.

[sizebot]

React: size: -2.3%, gzip: -3.1%

Details of bundled changes.

Comparing: 868d02d...d61c6cc

react

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
react.development.js	-0.0%	-0.0%	112.65 KB	112.65 KB	28.84 KB	28.84 KB	UMD_DEV
react.production.min.js	-2.3%	-3.1%	12.64 KB	12.35 KB	5.02 KB	4.87 KB	UMD_PROD
react.profiling.min.js	-2.2%	-2.8%	14.82 KB	14.5 KB	5.56 KB	5.4 KB	UMD_PROFILING
react.development.js	0.0%	-0.0%	72 KB	72 KB	18.93 KB	18.93 KB	NODE_DEV
react.production.min.js	0.0%	-0.1%	6.66 KB	6.66 KB	2.77 KB	2.77 KB	NODE_PROD
React-dev.js	0.0%	-0.0%	69.97 KB	69.97 KB	18.01 KB	18.01 KB	FB_WWW_DEV
React-prod.js	0.0%	-0.0%	17.32 KB	17.32 KB	4.53 KB	4.53 KB	FB_WWW_PROD
React-profiling.js	0.0%	-0.0%	17.32 KB	17.32 KB	4.53 KB	4.53 KB	FB_WWW_PROFILING

scheduler

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
scheduler-unstable_mock.development.js	0.0%	-0.0%	16.71 KB	16.71 KB	4.1 KB	4.1 KB	UMD_DEV
scheduler-tracing.profiling.min.js	0.0%	-0.1%	3.25 KB	3.25 KB	992 B	991 B	NODE_PROFILING
scheduler-unstable_mock.production.min.js	0.0%	-0.0%	4.73 KB	4.73 KB	1.98 KB	1.98 KB	UMD_PROD
Scheduler-dev.js	-0.4%	-0.1%	26.23 KB	26.11 KB	6.95 KB	6.94 KB	FB_WWW_DEV
Scheduler-prod.js	-21.3%	-15.2%	15.92 KB	12.54 KB	3.59 KB	3.05 KB	FB_WWW_PROD
scheduler-tracing.development.js	0.0%	-0.0%	11.59 KB	11.59 KB	2.98 KB	2.98 KB	NODE_DEV
scheduler-tracing.production.min.js	0.0%	-0.3%	728 B	728 B	382 B	381 B	NODE_PROD
scheduler-unstable_mock.development.js	0.0%	-0.0%	16.52 KB	16.52 KB	4.04 KB	4.04 KB	NODE_DEV
scheduler-unstable_mock.production.min.js	0.0%	-0.1%	4.72 KB	4.72 KB	1.92 KB	1.92 KB	NODE_PROD
SchedulerMock-dev.js	-1.5%	-1.3%	17.05 KB	16.8 KB	4.16 KB	4.11 KB	FB_WWW_DEV
scheduler.development.js	-0.0%	0.0%	25.63 KB	25.63 KB	6.84 KB	6.84 KB	NODE_DEV
scheduler.production.min.js	-5.7%	-7.1%	5.23 KB	4.93 KB	2.15 KB	1.99 KB	NODE_PROD

Generated by 🚫 dangerJS

[sebmarkbage]

Maybe we need to make sure this works on RN now?

[acdlite]

Let's go ahead and merge this?

[gaearon]

Lemme check RN. What are we looking for? Just that effects fire?

[sizebot]

React: size: -2.2%, gzip: -2.8%

Details of bundled changes.

Comparing: 79e46b6...1773240

react

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
react.development.js	-0.0%	0.0%	119.56 KB	119.56 KB	30.27 KB	30.27 KB	UMD_DEV
react.production.min.js	-2.2%	-2.8%	12.71 KB	12.43 KB	5.04 KB	4.9 KB	UMD_PROD
react.profiling.min.js	-1.8%	-2.6%	16.11 KB	15.83 KB	6.05 KB	5.9 KB	UMD_PROFILING
react.development.js	0.0%	-0.0%	73.12 KB	73.12 KB	19.25 KB	19.25 KB	NODE_DEV
react.production.min.js	0.0%	-0.0%	6.69 KB	6.69 KB	2.78 KB	2.78 KB	NODE_PROD
React-dev.js	0.0%	-0.0%	71.18 KB	71.18 KB	18.31 KB	18.31 KB	FB_WWW_DEV
React-prod.js	0.0%	0.0%	17.41 KB	17.41 KB	4.55 KB	4.56 KB	FB_WWW_PROD
React-profiling.js	0.0%	0.0%	17.41 KB	17.41 KB	4.55 KB	4.56 KB	FB_WWW_PROFILING

scheduler

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
scheduler-unstable_mock.development.js	0.0%	-0.0%	22.12 KB	22.12 KB	5.13 KB	5.13 KB	UMD_DEV
scheduler-tracing.profiling.min.js	0.0%	-0.1%	3.25 KB	3.25 KB	994 B	993 B	NODE_PROFILING
scheduler-unstable_mock.production.min.js	0.0%	-0.1%	4.73 KB	4.73 KB	1.98 KB	1.98 KB	UMD_PROD
Scheduler-dev.js	-0.4%	-0.1%	31.87 KB	31.76 KB	8 KB	7.99 KB	FB_WWW_DEV
Scheduler-prod.js	-21.1%	-15.1%	15.99 KB	12.61 KB	3.61 KB	3.06 KB	FB_WWW_PROD
Scheduler-profiling.js	-17.2%	-12.6%	19.62 KB	16.24 KB	4.3 KB	3.76 KB	FB_WWW_PROFILING
scheduler-tracing.development.js	0.0%	0.0%	11.72 KB	11.72 KB	3.03 KB	3.03 KB	NODE_DEV
scheduler-unstable_mock.production.min.js	0.0%	-0.1%	4.72 KB	4.72 KB	1.92 KB	1.92 KB	NODE_PROD
SchedulerMock-dev.js	-1.1%	-1.0%	22.5 KB	22.25 KB	5.21 KB	5.15 KB	FB_WWW_DEV
scheduler.development.js	-0.0%	0.0%	31.26 KB	31.26 KB	7.88 KB	7.89 KB	NODE_DEV
scheduler.production.min.js	-5.4%	-7.4%	5.29 KB	5 KB	2.16 KB	2 KB	NODE_PROD

Generated by 🚫 dangerJS against 1773240

[gaearon]

I tested on RN a bit. useEffect works.
The fallback implementation is the same with or without the flag, so that should be fine.

[brunolemos]

that should be fine

famous last words 😄

[phaistonian]

Is this change published on the latest or any of the pre-releases?