Add dynamic flags to React Native

[rickhanlonii]

Overview

This should allow RN to turn flags on/off.

They need this right now to temporarily turn off enableSyncDefaultUpdates.

[acdlite]

This should be a new file specific to RN, like './ReactFeatureFlags.native-fb-dynamic'.

Then you need to setup Jest to route to the correct file, like we do for www:

react/scripts/jest/setupTests.www.js

Lines 4 to 8 in f3337aa

	jest.mock(
	'ReactFeatureFlags',
	() => jest.requireActual('shared/forks/ReactFeatureFlags.www-dynamic'),
	{virtual: true}
	);

The trouble is that we don't have an RN specific test run. Could you move all our RN tests into their own Jest project, like we do for DevTools? That's the direction we're headed, where each renderer has its own project. Like how the yarn flow command works.

[rickhanlonii]

Ah right - I'm just going to hardcode the setting to false for now then to unblock and come back to this while working out how this flag works in www

[sizebot]

Comparing: f3337aa...9aff2c4

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	122.72 kB	122.72 kB	=	39.39 kB	39.39 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	129.30 kB	129.30 kB	=	41.48 kB	41.48 kB
facebook-www/ReactDOM-prod.classic.js	=	412.22 kB	412.22 kB	=	76.23 kB	76.24 kB
facebook-www/ReactDOM-prod.modern.js	=	400.29 kB	400.29 kB	=	74.32 kB	74.32 kB
facebook-www/ReactDOMForked-prod.classic.js	=	412.22 kB	412.22 kB	=	76.24 kB	76.24 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 9aff2c4