[MD settings] performance improvement on $i18n{} replacement
[MD settings] performance improvement on $i18n{} replacement

This CL improves the cpu performance on $i18n{} replacement.
The code has come up faster in each test.  While the benefit
varies, it averages around 10x faster than the current method.

BUG=506009

Review URL: https://codereview.chromium.org/1641683006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#372878}

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