Updating trunk VERSION from 4390.0 to 4391.0

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

Change-Id: Idf5cc4ed97c2a9b06d7927dd9114201a5047a971
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633427Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#844356}

chrome/VERSION

 MAJOR=90
 MINOR=0
-BUILD=4390
+BUILD=4391
 PATCH=0