GPU Memory: update unittest to reduce flakiness am: 6f63ce04c6 am: c26bc5a8d6 am: d77e088653

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/1472021

Change-Id: I90c71ec3af3a21df82efe8d2b474c8ef4f72d5a4