Updating trunk VERSION from 4006.0 to 4007.0

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

Change-Id: I38ecae21140dfecfdc0df66ce515a53db255ed52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980492Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#727335}

chrome/VERSION

 MAJOR=81
 MINOR=0
-BUILD=4006
+BUILD=4007
 PATCH=0