Fix the flaky test

[yuriy-fix]

Description

Test is flaky on smaller screen.

Expected outcome

Works the same way on all screens.

Actual outcome

Not working on MBP screen.

Live Demo

https://cdn.vaadin.com/vaadin-combo-box/4.2.0-alpha4/test/

Steps to reproduce

1. Open the test page.
2. Wait till test will fail.

Browsers Affected

• Chrome
• Firefox
• Safari
• Edge
• IE 11
• iOS Safari
• Android Chrome

[Haprog]

There are currently at least 4 different tests that can fail depending on viewport height.

These 2 tests fail with timeout when viewport height >= 749 px:

• keyboard.html > keyboard navigation > scrolling items > should scroll to focused item when opening overlay
• scrolling.html > scrolling > scrolling position > should make selected item visible after open

Fails with assertion failure when viewport height <= 166 px:

• keyboard.html > keyboard navigation > sanity checks for calculating visible item counts > should calculate items correctly when all items are visible

Fails with assertion failure when viewport height <= 499 px:

• filtering.html > filtering items > setting items when opened > should properly display all items in the selector

This means that atm. all tests can pass only if viewport height is in the range 500–748 px.

(tested with Chrome 74 on macOS 10.14.5)

[Haprog]

The failure of these two:

• keyboard.html > keyboard navigation > scrolling items > should scroll to focused item when opening overlay
• scrolling.html > scrolling > scrolling position > should make selected item visible after open

seems to be an actual bug. I opened a new issue about it here with more details: #815.

[Haprog]

Just noticed that it's not only about viewport height but also viewport width plays some role in these failures. E.g. on Chrome with DPR 2.2 the above filtering.html test fails also on viewport height 512px when the viewport width is less than 900px.