Introduce NavigatorWebDriver interface

third_party/WebKit/Source/core/frame/NavigatorWebDriver.idl

Index: third_party/WebKit/Source/core/frame/NavigatorWebDriver.idl
diff --git a/third_party/WebKit/Source/core/frame/NavigatorWebDriver.idl b/third_party/WebKit/Source/core/frame/NavigatorWebDriver.idl
new file mode 100644
index 0000000000000000000000000000000000000000..9dafe6e4577c62ea5e7d87b0d5c2d23a59482d71
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+++ b/third_party/WebKit/Source/core/frame/NavigatorWebDriver.idl
@@ -0,0 +1,12 @@
+// 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.
+
+// https://www.w3.org/TR/webdriver/#interface
+
+[
+    NoInterfaceObject, // Always used on target of 'implements'
+    Exposed=(Window),
+] interface NavigatorWebDriver {
+    [Unforgeable] readonly attribute boolean webdriver;
+};