Updating trunk VERSION from 4250.0 to 4251.0

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

Change-Id: I0c3348b5efb93c0e08d4ca4acc76a0dbb204e0c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2384319Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#803006}

chrome/VERSION

 MAJOR=87
 MINOR=0
-BUILD=4250
+BUILD=4251
 PATCH=0