Add WebUSB bindings and client interface [part 1]

Source/modules/webusb/NavigatorUSB.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/NavigatorUSB.h"
+
+#include "core/frame/Navigator.h"
+#include "modules/webusb/USB.h"
+
+namespace blink {
+
+// static

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

Drop the comment.

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

Done.

+NavigatorUSB& NavigatorUSB::from(Navigator& navigator)
+{
+    NavigatorUSB* supplement = static_cast<NavigatorUSB*>(HeapSupplement<Navigator>::from(navigator, supplementName()));
+    if (!supplement) {
+        supplement = new NavigatorUSB(navigator);
+        provideTo(navigator, supplementName(), supplement);
+    }
+    return *supplement;
+}
+
+// static

[haraken, 2015/07/30 11:26:51]

Drop the comment.

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

Done.

+USB* NavigatorUSB::usb(Navigator& navigator)
+{
+    return NavigatorUSB::from(navigator).usb();
+}
+
+USB* NavigatorUSB::usb()
+{
+    return m_usb.get();

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

.get() won't be needed.

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

Done.

+}
+
+DEFINE_TRACE(NavigatorUSB)
+{
+    visitor->trace(m_usb);
+    HeapSupplement<Navigator>::trace(visitor);
+}
+
+NavigatorUSB::NavigatorUSB(Navigator& navigator)
+    : m_usb(USB::create(*navigator.frame()))

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

Is it guaranteed that navigator.frame() returns a non-null frame?

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

That assumption seems to be made in a lot of places - whether or not it's
correct probably depends on context. It looks like frame() can only be null
after DOMWindowProperty::willDestroyGlobalObjectInFrame is called on the
Navigator instance.

In any case I've changed this so that m_usb will be null if navigator.frame() is
null upon NavigatorUSB construction. I think that should be OK.

+{
+}
+
+const char* NavigatorUSB::supplementName()
+{
+    return "NavigatorUSB";
+}
+
+} // namespace blink