Add WebUSB bindings and client interface

public/platform/modules/webusb/WebUSBClient.h

Index: public/platform/modules/webusb/WebUSBClient.h
diff --git a/public/platform/modules/webusb/WebUSBClient.h b/public/platform/modules/webusb/WebUSBClient.h
new file mode 100644
index 0000000000000000000000000000000000000000..dece4646a66a99aad35cbd7adde0c4565b26b26f
--- /dev/null
+++ b/public/platform/modules/webusb/WebUSBClient.h
@@ -0,0 +1,30 @@
+// 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 WebUSBClient_h
+#define WebUSBClient_h
+
+#include "public/platform/WebCallbacks.h"
+#include "public/platform/WebVector.h"
+
+namespace blink {
+
+class WebUSBDevice;
+struct WebUSBDeviceEnumerationOptions;
+struct WebUSBError;
+
+typedef WebCallbacks<WebVector<WebUSBDevice*>*, WebUSBError*> WebUSBClientGetDevicesCallbacks;
+
+class WebUSBClient {
+public:
+    virtual ~WebUSBClient() { }
+
+    // Enumerates available devices.
+    // Ownership of the WebUSBClientGetDevicesCallbacks is transferred to the client.
+    virtual void getDevices(const WebUSBDeviceEnumerationOptions&, WebUSBClientGetDevicesCallbacks*) = 0;
+};
+
+} // namespace blink
+
+#endif // WebUSBClient_h