Add presubmit check to prevent package boundary violations.

tools-webrtc/testdata/subdir/subdir2/BUILD.gn

Index: tools-webrtc/testdata/subdir/subdir2/BUILD.gn
diff --git a/tools-webrtc/testdata/subdir/subdir2/BUILD.gn b/tools-webrtc/testdata/subdir/subdir2/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..c6f45307a2447d6a587050bfc4bf361dd25b3b21
--- /dev/null
+++ b/tools-webrtc/testdata/subdir/subdir2/BUILD.gn
@@ -0,0 +1,23 @@
+# 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.
+
+static_library("subdir2") {
+  sources = [
+    "dummy3.cc",
+    "dummy3.h",
+  ]
+}
+
+# Testing that this work with indentation.
+if (is_win) {
+  source_set("dummy_test_support") {
+    sources = [
+      "dummy_main.cc",
+    ]
+  }
+}