Fix NQE (NetworkQualityEstimator) tests.
Fix NQE (NetworkQualityEstimator) tests.

PercentileSameTimestamps has been failing on Valgrind
because of small differences in the timestamps (that were
being compared).

TestLRUCacheMaximumSize had been failing on Windows
because multiple networks will have the same timestamp.
So, networks added earlier may remain the cache while the
networks added later may get evicted (because both of them
have the same timestamp). This was causing the test
to fail.

BUG=513910, 510689

Review URL: https://codereview.chromium.org/1259833002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#340713}

ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend