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..d8b94cfd068162d1171fdb01af99ef5b210087df
--- /dev/null
+++ b/Source/modules/webusb/USBAlternateInterface.idl
@@ -0,0 +1,17 @@
+// 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.
+
+[
+    Constructor(USBInterface deviceInterface, octet alternateIndex),
+    RaisesException=Constructor,
+    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;
+};