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This avoids some heap allocations and allows many callsites to
be more concise.

Bug: 646113
Bug: Internal b/117125296
Test: all the unittests I can run on desktop, CQ

Merge-With: eureka-internal/206552
Merge-With: eureka-internal/206533

Change-Id: I48505d8c2a693c7e36616d47b6aad2348db115a6
Reviewed-on: https://chromium-review.googlesource.com/c/1256214Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596055}