Moving check_package_boundaries to the presubmit checks directory

tools_webrtc/testdata/multiple_errors_multiple_targets/BUILD.gn

-# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
-#
-# Use of this source code is governed by a BSD-style license
-# that can be found in the LICENSE file in the root of the source
-# tree. An additional intellectual property rights grant can be found
-# in the file PATENTS.  All contributing project authors may
-# be found in the AUTHORS file in the root of the source tree.
-
-target("dummy_target_ok") {
-  sources = [
-    "dummy_source.cc",
-    "dummy_source.h",
-  ]
-}
-
-target("error_1") {
-  sources = [
-    "subpackage1/dummy_subpackage1.cc",
-    "subpackage1/dummy_subpackage1.h",
-  ]
-}
-
-target("error_2") {
-  sources = [
-    "subpackage1/dummy_subpackage2.cc",
-    "subpackage1/dummy_subpackage2.h",
-  ]
-}