DNR: Add documentation for "removeHeaders" rules.

This CL adds public documentation for "removeHeaders" rules.

BUG=947591

Change-Id: I56d7f11e900d37c7606c6b1aabff928fdd27984c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1576258
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653867}
2 files changed