Patch #1 of multiple. Add webauth .mojom and initial usage of makeCredential.

components/webauth/BUILD.gn

Index: components/webauth/BUILD.gn
diff --git a/components/webauth/BUILD.gn b/components/webauth/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..80da9afb1b310f04d338c8860971810f173bcacf
--- /dev/null
+++ b/components/webauth/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.
+
+import("//mojo/public/tools/bindings/mojom.gni")
+
+mojom("authenticator") {
+  sources = [
+    "authenticator.mojom",
+  ]
+
+  public_deps = [
+    "//mojo/common:common_custom_types",
+  ]
+}