Updating trunk VERSION from 4001.0 to 4002.0

# This is an automated release commit.
# Do not revert without consulting chrome-pmo@google.com.
NOAUTOREVERT=true
TBR=cmasso@chromium.org

Change-Id: Ieb26af4ed83ef1a33e084f08746289fc0595f90c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1975057Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#726257}

chrome/VERSION

 MAJOR=81
 MINOR=0
-BUILD=4001
+BUILD=4002
 PATCH=0