Emilis Baliukonis 232517a574 Implement nativePerformanceNow to improve Profiler API results (#27885) ... Summary: When experimenting with React Profiler API (https://reactjs.org/docs/profiler.html), I noticed that durations are integers without a debugger, but they are doubles with higher precision when debugger is attached. After digging into React Profiler code, I found out that it's using `performance.now()` to accumulate execution times of individual units of work. Since this method does not exist in React Native, it falls back to Javascript `Date`, leading to imprecise results. This PR introduces `global.nativePerformanceNow` function which returns precise native time, and a very basic `performance` polyfill with `now` function. This will greatly improve React Profiler API results, which is essential for profiling and benchmark tools. Solves https://github.com/facebook/react-native/issues/27274 ## Changelog [General] [Added] - Implement `nativePerformanceNow` and `performance.now()` Pull Request resolved: https://github.com/facebook/react-native/pull/27885 Test Plan: ``` const initialTime = global.performance.now(); setTimeout(() => { const newTime = global.performance.now(); console.warn('duration', newTime - initialTime); }, 1000); ``` ### Android + Hermes  ### Android + JSC  ### iOS  Reviewed By: ejanzer Differential Revision: D19888289 Pulled By: rickhanlonii fbshipit-source-id: ab8152382da9aee9b4b3c76f096e45d40f55da6c		2020-03-31 10:23:51 -07:00
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Devtools	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
SegmentFetcher	TM JS: Revert to import from TurboModuleRegistry.js	2019-11-08 11:44:16 -08:00
Timers	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
__mocks__	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
__tests__	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
ExceptionsManager.js	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
InitializeCore.js	Implement nativePerformanceNow to improve Profiler API results (#27885)	2020-03-31 10:23:51 -07:00
NativeExceptionsManager.js	Exact-by-default codemod for react-native-github	2019-11-21 09:42:57 -08:00
ReactFiberErrorDialog.js	Convert easy files to flow strict-local	2019-12-05 16:06:46 -08:00
ReactNativeVersion.js	Update copyright headers to yearless format	2018-09-11 15:33:07 -07:00
ReactNativeVersionCheck.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
checkNativeVersion.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
polyfillPromise.js	Convert easy files to flow strict-local	2019-12-05 16:06:46 -08:00
setUpAlert.js	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
setUpBatchedBridge.js	Backwards-compatible implementation for registerCallableModule	2019-12-17 18:38:57 -08:00
setUpDeveloperTools.js	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
setUpErrorHandling.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
setUpGlobals.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
setUpNavigator.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
setUpPerformance.js	Implement nativePerformanceNow to improve Profiler API results (#27885)	2020-03-31 10:23:51 -07:00
setUpReactDevTools.js	Do not explicitly include ".js" in Library imports (#28311)	2020-03-17 02:11:53 -07:00
setUpReactRefresh.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
setUpRegeneratorRuntime.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
setUpSegmentFetcher.js	Exact-by-default codemod for react-native-github	2019-11-21 09:42:57 -08:00
setUpSystrace.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00
setUpTimers.js	Back out "Upgrade Prettier from 1.17 to 2.0.2."	2020-03-24 21:47:35 -07:00
setUpXHR.js	Tidy up license headers [2/n]	2019-10-16 10:06:34 -07:00