Add WebUSB bindings and client interface [part 1]

Source/modules/webusb/USB.cpp

+// 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.
+
+#include "config.h"
+#include "modules/webusb/USB.h"
+
+#include "modules/webusb/USBDeviceEnumerationOptions.h"
+#include "modules/webusb/USBDeviceFilter.h"
+#include "public/platform/modules/webusb/WebUSBClient.h"
+#include "public/platform/modules/webusb/WebUSBDeviceEnumerationOptions.h"
+#include "public/platform/modules/webusb/WebUSBDeviceFilter.h"

[haraken, 2015/07/30 11:26:52]

Some of the header files won't be necessary in this CL, but I'm ok with adding
them in this CL.

[Ken Rockot(use gerrit already), 2015/07/30 18:06:54]

Acknowledged.

+
+namespace blink {
+
+USB::USB(LocalFrame& frame)
+    : m_controller(USBController::from(frame))
+{
+}
+
+ScriptPromise USB::getDevices(ScriptState* scriptState, const USBDeviceEnumerationOptions& options)
+{
+    ASSERT_NOT_REACHED();
+}
+
+DEFINE_TRACE(USB)
+{
+#if ENABLE(OILPAN)

[haraken, 2015/07/30 11:26:52]

This wouldn't be necessary.

[Ken Rockot(use gerrit already), 2015/07/30 18:06:54]

Done.

+    visitor->trace(m_controller);
+#endif
+}
+
+} // namespace blink