Add WebUSB bindings and client interface [part 1]

Source/modules/webusb/USB.idl

Index: Source/modules/webusb/USB.idl
diff --git a/Source/modules/webusb/USB.idl b/Source/modules/webusb/USB.idl
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index 0000000000000000000000000000000000000000..000aa35d140a2e379b95556935ae91097ee62aeb
--- /dev/null
+++ b/Source/modules/webusb/USB.idl
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+// 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.
+
+// http://reillyeon.github.io/webusb/#device-enumeration
+
+[
+    GarbageCollected,
+    NoInterfaceObject,
+    RuntimeEnabled=WebUSB,
+] interface USB {
+    [CallWith=ScriptState] Promise<sequence<USBDevice>> getDevices(USBDeviceEnumerationOptions options);
+};