Updating trunk VERSION from 4420.0 to 4421.0

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

Change-Id: I4d6b491e1e7f05004924d383e816de0cd1f46085
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2696090
Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#854140}

chrome/VERSION

@@ -1,4 +1,4 @@
 MAJOR=90
 MINOR=0
-BUILD=4420
+BUILD=4421
 PATCH=0