Updating trunk VERSION from 4039.0 to 4040.0

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

Change-Id: If8462b5978f33b93415a947ea7c6647b425a3547
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2020411Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#735259}

chrome/VERSION

 MAJOR=81
 MINOR=0
-BUILD=4039
+BUILD=4040
 PATCH=0