“Lightmap Overlap” mode is not available for Scene Visualisation.

Steps to Reproduce:
1. Open LightSettings Window from Window Menu > Lighting > Settings
2. Enable Real Time Global Illumination
3. Enable Baked Global Illumination under Mixed Lighting
4. Enable Auto Generate
5. Go to Scene View

Expected Result :
Visualisation Modes such as Light Overlap, Lightmap Indicies should be available for selection.

Actual Result:
Visualisation Modes such as Light Overlap, Lightmap Indices are missing

Working fine on:
2018.1.0a6, 2018.1.0a5, 2017.3.0f3, 2017.3.0f1

Reproducible on:
2018.1.0b1, 2018.1.0a7

Environment :
Occurring on Windows and Mac.