Add license checker config and kokoro presubmit

`license-checker` is a tool that verifies each file has contains a permitted license header.

See https://github.com/ben-clayton/license-checker for more information.

Also add missing licenses to presubmit scripts.

kokoro/license-check/presubmit-docker.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# Copyright 2020 The Marl Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -e # Fail on any error.
+
+license-checker

kokoro/license-check/presubmit.cfg

@@ -0,0 +1,4 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+build_file: "cppdap/kokoro/license-check/presubmit.sh"
+

kokoro/license-check/presubmit.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -e # Fail on any error.
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd )"
+ROOT_DIR="$( cd "${SCRIPT_DIR}/../.." >/dev/null 2>&1 && pwd )"
+
+docker run --rm -i \
+  --volume "${ROOT_DIR}:${ROOT_DIR}" \
+  --volume "${KOKORO_ARTIFACTS_DIR}:/mnt/artifacts" \
+  --workdir "${ROOT_DIR}" \
+  --entrypoint "${SCRIPT_DIR}/presubmit-docker.sh" \
+  "gcr.io/shaderc-build/radial-build:latest"