printing: add missing header files to BUILD.gn

https://docs.google.com/spreadsheets/d/15az3FMl-jAS0mx4E9XVSBVHVpmEzo-9EAGY0ywe7bZs/edit#gid=0

https://groups.google.com/a/chromium.org/d/topic/chromium-dev/1kK45mVemBc/discussion

BUG=661774
R=thestig@chromium.org

Review-Url: https://codereview.chromium.org/2774753005
Cr-Commit-Position: refs/heads/master@{#459626}
2 files changed