Steps to reproduce:
1. download and open minimal repro project
2. move around view, observe white cubes do not flicker when behind black cube
3. select lightweight render pipeline asset (in project tab)
4. enable SRP Batcher (in inspector tab)
5. move around view, observe white cubes flickering when behind black cube

Expected result: No flickering; SRP batcher should only batch draw calls which use the same stencil ref value
Actual result: Flickering; white cube draw calls are batched despite different stencil ref values

Note:
- the draw calls use a randomly-selected Stencil ref value from the batched materials which causes flickering
- batched materials (white cubes) in the small repro use Stencil Ref 2 and 3

Reproducible with: 2019.2.10f1 (LWRP 6.9.2), 2019.2.3f1 (LWRP 6.9.0)
Not reproducible with: 2019.3.0a7 (LWRP 6.9.2)