Clarify |Namespaces| is always non-null in MarkupAccumulator

- Change |Namespaces*| arguments to |Namespaces&|.
- Remove unnecessary |Namespaces| pointer setup code

This CL has no behavior changes.

Bug: 927166
Change-Id: Id00e3df7a7e120718f9e454c7850079b4a7062f2
Reviewed-on: https://chromium-review.googlesource.com/c/1451696
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628680}
3 files changed