Add WebUSB bindings and client interface

Source/modules/webusb/USBAlternateInterface.idl

Index: Source/modules/webusb/USBAlternateInterface.idl
diff --git a/Source/modules/webusb/USBAlternateInterface.idl b/Source/modules/webusb/USBAlternateInterface.idl
new file mode 100644
index 0000000000000000000000000000000000000000..73515c1d3fd372342df419eac01c41a1a8c5821f
--- /dev/null
+++ b/Source/modules/webusb/USBAlternateInterface.idl
@@ -0,0 +1,15 @@
+// Copyright 2015 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.
+
+[
+    GarbageCollected,
+    RuntimeEnabled=WebUSB,
+] interface USBAlternateInterface {
+    readonly attribute octet alternateSetting;
+    readonly attribute octet interfaceClass;
+    readonly attribute octet interfaceSubclass;
+    readonly attribute octet interfaceProtocol;
+    readonly attribute DOMString? interfaceName;
+    readonly attribute sequence<USBEndpoint> endpoints;
+};