Updating trunk VERSION from 3869.0 to 3870.0

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

Change-Id: Ia504baed1d1a613fb58b06c2655093beb3115c89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724836Reviewed-by: chrome-release-bot@chromium.org <chrome-release-bot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682125}

chrome/VERSION

 MAJOR=78
 MINOR=0
-BUILD=3869
+BUILD=3870
 PATCH=0