Updating trunk VERSION from 4308.0 to 4309.0

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

Change-Id: Iec430597f241b6859632c4e6fd47a8d71a702d61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2508347Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#822503}

chrome/VERSION

 MAJOR=88
 MINOR=0
-BUILD=4308
+BUILD=4309
 PATCH=0