Use Check rather than if peek() + Expect/Consume

Change-Id: I5bc98288a751234117a2708c17dbb68008af5838
Reviewed-on: https://chromium-review.googlesource.com/c/1261144Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56376}