Add WebUSB bindings and client interface [part 1]

Source/modules/webusb/USBDevice.idl

Index: Source/modules/webusb/USBDevice.idl
diff --git a/Source/modules/webusb/USBDevice.idl b/Source/modules/webusb/USBDevice.idl
new file mode 100644
index 0000000000000000000000000000000000000000..dde7ad4bf8eeba7a570b04ce0760864d1930bf87
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+++ b/Source/modules/webusb/USBDevice.idl
@@ -0,0 +1,12 @@
+// 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-usage
+
+[
+    GarbageCollected,
+    RuntimeEnabled=WebUSB,
+] interface USBDevice {
+    readonly attribute DOMString guid;
+};