Add Digital Asset Links verification for postMessage API

components/digital_asset_links/BUILD.gn

Index: components/digital_asset_links/BUILD.gn
diff --git a/components/digital_asset_links/BUILD.gn b/components/digital_asset_links/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..245d925fa0e326847509ac062be879ee0bc9332a
--- /dev/null
+++ b/components/digital_asset_links/BUILD.gn
@@ -0,0 +1,15 @@
+# Copyright 2017 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("digital_asset_links") {
+  sources = [
+    "digital_asset_links_handler.cc",
+    "digital_asset_links_handler.h",
+  ]
+
+  deps = [
+    "//base",
+    "//net",
+  ]
+}