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https://google.github.io/styleguide/cppguide.html#Namespace_Names
> Namespace names are all lower-case.

This CL has no behavior changes.

Bug: 889726
Change-Id: I6e561ba5f0e92758fb2922bd8e41c4feb70f2203
Reviewed-on: https://chromium-review.googlesource.com/c/1301696Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Hwanseung Lee <hs1217.lee@samsung.com>
Cr-Commit-Position: refs/heads/master@{#603167}