Eliminate determinism in `base_test.js#testNow` causing flakiness.
Eliminate determinism in `base_test.js#testNow` causing flakiness.

RELNOTES: N/A

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google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,google/closure-library,google/closure-library,google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,google/closure-library