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..a5fe4cc030757bda8cdc77091c5c70de0db1730e
--- /dev/null
+++ 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 {
+    readonly attribute boolean webdriver;
+};