Update documentation to allow owners of public APIs that are used throughout the codebase to Owners-Override changes across the source tree.

Unlike LSC which is meant for work that spans dozens of CLs, this new change is meant for one-off CLs. It's similar to google3's global approvals mechanism.

base, build, blink, content and url were chosen as an initial set because they are used in many top level directories and are frequently changing.

Also add "set noparent" to top level directories to avoid inadvertent +1s from src/OWNERS bypass owners reviews sometimes.

Change-Id: Iaa397a5e09174139af21fee34dca390de132e216
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2688805
Auto-Submit: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#857391}

diff --git a/media/OWNERS b/media/OWNERS
index 6919903..79f898d 100644
--- a/media/OWNERS
+++ b/media/OWNERS

@@ -8,6 +8,7 @@
 # and to load balance. Only use OWNERS in this file for these subdirectories
 # when doing refactorings and general cleanups.
 
+set noparent
 chcunningham@chromium.org
 dalecurtis@chromium.org
 jrummell@chromium.org