Updating trunk VERSION from 4239.0 to 4240.0

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

Change-Id: I90c107da4830a4459f7319f957513cba15fe5ff0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366472Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#799978}

chrome/VERSION

 MAJOR=86
 MINOR=0
-BUILD=4239
+BUILD=4240
 PATCH=0