TransformFeedbackTest: Give enough vertex attributes
TransformFeedbackTest: Give enough vertex attributes

BUG=angleproject:1570

Change-Id: I6d148c6ce22f3b8266257b25c7f5b676a13c5c92
Reviewed-on: https://chromium-review.googlesource.com/402931
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Commit-Queue: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

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