Add optional public header checking to GN build

third_party/modp_b64/BUILD.gn

Index: third_party/modp_b64/BUILD.gn
diff --git a/tools/gn/secondary/third_party/modp_b64/BUILD.gn b/third_party/modp_b64/BUILD.gn
similarity index 96%
rename from tools/gn/secondary/third_party/modp_b64/BUILD.gn
rename to third_party/modp_b64/BUILD.gn
index 539abe1580a16519a900773815556b20f69de590..5598f12f18209f028e7108ac5a9101e99343854c 100644
--- a/tools/gn/secondary/third_party/modp_b64/BUILD.gn
+++ b/third_party/modp_b64/BUILD.gn
@@ -1,11 +1,11 @@
-# Copyright (c) 2013 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.
-
-static_library("modp_b64") {
-  sources = [
-    "modp_b64.cc",
-    "modp_b64.h",
-    "modp_b64_data.h",
-  ]
-}
+# Copyright (c) 2013 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.
+
+static_library("modp_b64") {
+  sources = [
+    "modp_b64.cc",
+    "modp_b64.h",
+    "modp_b64_data.h",
+  ]
+}