Updating trunk VERSION from 3872.0 to 3873.0

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

Change-Id: I99c611eb02d9ddca7c70b3f4fc6fb7fb78c3e9c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1732729Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#683459}

chrome/VERSION

 MAJOR=78
 MINOR=0
-BUILD=3872
+BUILD=3873
 PATCH=0