[Animation Worklet] Clean up WorkletAnimation unittest

 - Use SimulateFrame everywhere
 - Introduce EXPECT_TIME_NEAR with uniform error value
 - Use CurrentTime() directly instead of generating state

Changes: 
Change-Id: I1ea855443ff21d8152bb9766f021af01e6cc59d8
Reviewed-on: https://chromium-review.googlesource.com/c/1461824
Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630765}
2 files changed