InstancingTest: fix a stack overflow.
InstancingTest: fix a stack overflow.

BUG=angleproject:1661

Change-Id: Iac7af4aed2782ab839922281d29f1a9861a334e3
Reviewed-on: https://chromium-review.googlesource.com/419758
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

ppy/angle,ecoal95/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,ppy/angle,ecoal95/angle,ppy/angle,ecoal95/angle,ecoal95/angle,MSOpenTech/angle,ecoal95/angle,MSOpenTech/angle