[lacros] Add presubmit for build/lacros directory

This CL ensures that all tests are run when changes are made to
build/lacros to avoid accidental breakages.

Change-Id: I8d4d056d3e551b7786249f2be43d6513c3422af9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488980Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819244}

build/lacros/PRESUBMIT.py

+# Copyright (c) 2020 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Presubmit script for changes affecting //build/lacros"""
+
+
+def _CommonChecks(input_api, output_api):
+  tests = input_api.canned_checks.GetUnitTestsInDirectory(
+      input_api, output_api, '.', [r'^.+_test\.py$'])
+  return input_api.RunTests(tests)
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CommonChecks(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return _CommonChecks(input_api, output_api)