Fix smooth scrolling on old devices (SDK >=16)

[cgiote]

Environment

React Native Environment Info:
System:
OS: Linux 4.15 Ubuntu 18.04.1 LTS (Bionic Beaver)
CPU: (4) x64 Intel(R) Core(TM) i5-7300U CPU @ 2.60GHz
Memory: 1.12 GB / 15.55 GB
Shell: 4.4.19 - /bin/bash
Binaries:
Node: 8.10.0 - /usr/bin/node
Yarn: 1.13.0 - /usr/local/bin/yarn
npm: 3.5.2 - /usr/bin/npm
SDKs:
Android SDK:
API Levels: 16, 19, 22, 23, 24, 25, 26, 27, 28
Build Tools: 23.0.1, 23.0.3, 25.0.0, 25.0.2, 25.0.3, 26.0.1, 26.0.3, 27.0.3, 28.0.2, 28.0.3
System Images: android-16 | Google APIs Intel x86 Atom, android-19 | Google APIs Intel x86 Atom, android-24 | Google Play Intel x86 Atom, android-27 | Google APIs Intel x86 Atom, android-28 | Intel x86 Atom_64, android-28 | Google APIs Intel x86 Atom, android-28 | Google Play Intel x86 Atom
npmPackages:
react: 16.8.6 => 16.8.6
react-native: git+https://github.com/facebook/react-native.git#v0.59.5 => 0.59.5
npmGlobalPackages:
react-native-cli: 2.0.1
react-native-git-upgrade: 0.2.7

Description

The workaround implemented in #21117 tries to fix
https://issuetracker.google.com/issues/112385925 scroll direction (according to the latest comments, the scroll direction problem has been reverted in security patches so not sure if the workaround is still valid).

But... proposed solution in fling method is using signum which leads to zero computedVelocityY in case of zero mOnScrollDispatchHelper.getYFlingVelocity() on old devices(Samsung s4 mini) even when real velocityY is non zero

final int correctedVelocityY = (int)(Math.abs(velocityY) * Math.signum(mOnScrollDispatchHelper.getYFlingVelocity()));

Proposed solution is to take signum from original velocityY in case of zero

float signum = Math.signum(mOnScrollDispatchHelper.getYFlingVelocity());
if (signum == 0) {
  signum = Math.signum(velocityY);
}
final int correctedVelocityY = (int)(Math.abs(velocityY) * signum);

The symptoms are the same as described in issue #22925, but proposed workaround doesn't work.

Changelog

[Android][fixed] - Fix smooth scrolling on old devices (SDK >=16)

Test Plan

Install and test on old device. Works on Samsung S4 mini

[pull-bot]

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[cpojer]

Thank you!

[facebook-github-bot]

@cpojer is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by Pavel Rotek in 67be819.

^{When will my fix make it into a release? | Upcoming Releases}