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This CL renames the HeaderPainter because it does much more than
painting which has become confusing. This is a precursor CL to
https://chromium-review.googlesource.com/c/chromium/src/+/768601.

Bug: 762401
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_dbg_ng
Change-Id: Ie41fa68c8b4559e258eac6eee957cc059794bd96
Reviewed-on: https://chromium-review.googlesource.com/774058Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517265}