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

[haraken, 2015/07/30 20:17:59]

Actually I'm not sure if we should expect that NavigatorUSB::from() gets called
for a frame that is already detached. If you think that is not an expected
situation, you can change this to ASSERT(navigator.frame()).

[Ken Rockot(use gerrit already), 2015/07/30 21:10:34]

OK thought maybe this was true. Done.

[Ken Rockot(use gerrit already), 2015/07/30 23:23:05]

So actually there are layout tests which seem to exercise this possibility
(fast/dom/navigator-detached-no-crash.html for one). I've gone back to not
ASSERTing, and letting m_usb remain null in that case.

+        m_usb = USB::create(*navigator.frame());
+}
+
+const char* NavigatorUSB::supplementName()
+{
+    return "NavigatorUSB";
+}
+
+} // namespace blink