Updating trunk VERSION from 3520.0 to 3521.0

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

Change-Id: Ifc3b27a5ffc4d212dae7de39c99f48d9d60908bd
Reviewed-on: https://chromium-review.googlesource.com/1171992Reviewed-by: chrome-release-bot@chromium.org <chrome-release-bot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582467}

chrome/VERSION

 MAJOR=70
 MINOR=0
-BUILD=3520
+BUILD=3521
 PATCH=0