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And mention @RemovableInRelease and @CheckDiscard

Change-Id: I0de0fa818af5910bd4147985f6cee21da3c34ff9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1890844
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711286}