VariablePacker_test.cpp

The other one UnrollFlatten_test.cpp crashes.

BUG=
TEST=angle_unittests

Change-Id: I78e6e81e9b61f2a1599a5a0601b5b76165b180de
Reviewed-on: https://chromium-review.googlesource.com/295767Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tested-by: Zhenyao Mo <zmo@chromium.org>