Steps to reproduce:
1. Open user's attached project.
2. Open the scene called "CarTutAlt".
3. In toolbar press play button.
--- Note that everything runs smoothly.
4. Build and run this project using WebGL platform.
--- Note that screen this time looks black.

Reproduced in: 5.3.4f1, 5.4.0b19. (Also reproducible using Windows).

Some observations:
Deselecting "Motion Blur Edge" script solved this issue.
Steps to reproduce:
1. After deleting "Main_camera" in hierarchy window and adding it again you can now deselect "Motion Blur Edge" script attached to "Main_Camera". Deselect it.
2. Also in "Main Camera" inspector there is "Car Camera" script. In this script "Target" line add "Cog" object.
3. Build and run this project using WebGl platform. There are no issues right now.