How to reproduce:
1. Open the attached project ("case_1189110-Button_Test.zip")
2. Open the repro scene ("SampleScene")
3. Enter Play Mode
4. Click on the sprite object and notice how it rotates after receiving OnMouseDown event
5. Exit Play Mode
6. Make a WebGL build and run it
7. Click on the sprite object again

Expected results: The sprite is rotated in OnMouseDown event the same way as in the Editor
Actual results: The sprite is not rotated as OnMouseDown is not called when clicking on the object

Reproducible with: 2019.2.0a7, 2019.2.9f1, 2019.3.0b6, 2020.1.0a8
Not reproducible with: 2017.4.33f1, 2018.4.11f1, 2019.2.0a6

Notes:
1. OnMouseEnter and OnMouseExit events are also not called
2. Adding Event System in the scene fixes the issue in some cases
3. Disabling Engine Code Stripping also fixes the issue