Do not encode single byte characters with \uXXXX.

BUG=chromium:895974

Change-Id: If8e0bdb19d326228a7d3d0c9559d4457c8bfd270
Reviewed-on: https://chromium-review.googlesource.com/c/1292679Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56835}