Updating trunk VERSION from 4238.0 to 4239.0

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

Change-Id: I171b3d6aafc73c402f7b287cf0293363c72f9f98
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2363261Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#799470}

chrome/VERSION

 MAJOR=86
 MINOR=0
-BUILD=4238
+BUILD=4239
 PATCH=0