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This CL uses ResourceTiming API to speed up the test cases while
avoiding flakiness.

Bug: 779965
Change-Id: I40dc2fae470df296c87c12e432fc7fc7644cc40a
Reviewed-on: https://chromium-review.googlesource.com/923625
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537664}