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Some methods appeared to have left off references or that are
needlessly making copies. This CL converts these methods, only in unit
tests, to pass by reference.

Change-Id: I85c5b943e4c2ae0324e9170a08e0428325c3da0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863075Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Kevin Bailey <krb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706591}