Add WebUSB bindings and client interface

public/platform/modules/webusb/WebUSBError.h

Index: public/platform/modules/webusb/WebUSBError.h
diff --git a/public/platform/modules/webusb/WebUSBError.h b/public/platform/modules/webusb/WebUSBError.h
new file mode 100644
index 0000000000000000000000000000000000000000..d9a636e2b46900c584755be75935bd2aa37eefe7
--- /dev/null
+++ b/public/platform/modules/webusb/WebUSBError.h
@@ -0,0 +1,34 @@
+// 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.
+
+#ifndef WebUSBError_h
+#define WebUSBError_h
+
+#include "public/platform/WebString.h"
+
+namespace blink {
+
+// Error object used to create DOMExceptions when a Web USB request cannot be
+// satisfied.
+struct WebUSBError {
+    enum ErrorType {
+        DeviceError,
+        SecurityError,
+        ServiceError,
+        TransferError,
+    };
+
+    WebUSBError(ErrorType errorType, const WebString& message)
+        : errorType(errorType)
+        , message(message)
+    {
+    }
+
+    ErrorType errorType;
+    WebString message;
+};
+
+} // namespace blink
+
+#endif // WebUSBError_h