Updating trunk VERSION from 3538.0 to 3539.0 and incrementing major version to 71

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

Change-Id: I1a44dfd5f1535fa36388030b6291aac4f87667a0
Reviewed-on: https://chromium-review.googlesource.com/1198311Reviewed-by: chrome-release-bot@chromium.org <chrome-release-bot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587928}

chrome/MAJOR_BRANCH_DATE

-MAJOR_BRANCH_DATE=2018-07-20
+MAJOR_BRANCH_DATE=2018-08-31

chrome/VERSION

-MAJOR=70
+MAJOR=71
 MINOR=0
-BUILD=3538
+BUILD=3539
 PATCH=0