Add WebAuthn bindings and client interface.

third_party/WebKit/Source/modules/webauth/AuthenticationClientData.idl

Index: third_party/WebKit/Source/modules/webauth/AuthenticationClientData.idl
diff --git a/third_party/WebKit/Source/modules/webauth/AuthenticationClientData.idl b/third_party/WebKit/Source/modules/webauth/AuthenticationClientData.idl
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+++ b/third_party/WebKit/Source/modules/webauth/AuthenticationClientData.idl
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+// Copyright 2016 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.
+
+// https://w3c.github.io/webauthn/#sec-client-data
+
+dictionary AuthenticationClientData {
+    required DOMString challenge;
+    required DOMString origin;
+    required AlgorithmIdentifier hashAlg;
+    DOMString tokenBinding;
+    AuthenticationExtensions extensions;
+};