Update CookieNotificationBridge documentation to better reflect behavior.

From documentation on -[NSNotificationCenter addObserverForName:...]:
If you pass nil, the block is run synchronously on the posting thread.

Change-Id: Ib036764cb144d74750e9e1878d0cf7f239e25f7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626390
Auto-Submit: John Wu <jzw@chromium.org>
Reviewed-by: Mohammad Refaat <mrefaat@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663057}
1 file changed