kokoro: add initial presubmit script and config

BUG=b:73822503
TEST=run kokoro presubmit

Change-Id: Id128de2300a76f8a359521c83b371e9b743bc71b
Reviewed-on: https://chromium-review.googlesource.com/964601
Commit-Ready: Stephen Barber <smbarber@chromium.org>
Tested-by: Stephen Barber <smbarber@chromium.org>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>

kokoro/build.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# Copyright 2018 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+set -ex
+
+main() {
+    if [ -z "${KOKORO_ARTIFACTS_DIR}" ]; then
+        echo "This script must be run in kokoro"
+        exit 1
+    fi
+
+    local src_root="${KOKORO_ARTIFACTS_DIR}"/git/crosvm
+
+    return 0
+}
+
+main "$@"

kokoro/presubmit.cfg

@@ -0,0 +1,3 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+build_file: "crosvm/kokoro/build.sh"