Updating trunk VERSION from 4128.0 to 4129.0

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

Change-Id: Id199e13d0bff53e3fb4836d92fb72e61e7097091
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2167419Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#762719}

chrome/VERSION

 MAJOR=84
 MINOR=0
-BUILD=4128
+BUILD=4129
 PATCH=0