Add WebUSB bindings and client interface [part 1]

Source/modules/webusb/USBController.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/USBController.h"
+
+#include "platform/RuntimeEnabledFeatures.h"
+#include "public/platform/modules/webusb/WebUSBClient.h"
+
+namespace blink {
+
+USBController::~USBController()
+{
+}
+
+void USBController::provideTo(LocalFrame& frame, WebUSBClient* client)
+{
+    ASSERT(RuntimeEnabledFeatures::webUSBEnabled());
+    USBController* controller = new USBController(frame, client);
+    WillBeHeapSupplement<LocalFrame>::provideTo(frame, supplementName(), adoptPtrWillBeNoop(controller));
+}
+
+USBController* USBController::from(LocalFrame& frame)

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

Can we add an ASSERT to verify that the from doesn't return a nullptr? (i.e.,
provideTo should have been called before we reach here.)

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

Done.

+{
+    return static_cast<USBController*>(WillBeHeapSupplement<LocalFrame>::from(frame, supplementName()));
+}
+
+const char* USBController::supplementName()
+{
+    return "USBController";
+}
+
+USBController::USBController(LocalFrame& frame, WebUSBClient* client)
+    : LocalFrameLifecycleObserver(&frame)
+    , m_client(client)
+{
+}
+
+void USBController::willDetachFrameHost()
+{
+    m_client = nullptr;
+}
+
+DEFINE_TRACE(USBController)
+{
+    WillBeHeapSupplement<LocalFrame>::trace(visitor);
+    LocalFrameLifecycleObserver::trace(visitor);
+}
+
+} // namespace blink