Implement enumerateDevices() according to spec.

Source/modules/mediastream/NavigatorUserMedia.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/mediastream/NavigatorUserMedia.h"
+
+#include "core/frame/Navigator.h"
+#include "modules/mediastream/MediaDevices.h"
+#include "platform/Logging.h"
+
+namespace blink {
+
+NavigatorUserMedia::NavigatorUserMedia()
+    : m_mediaDevices(MediaDevices::create())
+{
+}
+
+const char* NavigatorUserMedia::supplementName()
+{
+    return "NavigatorUserMedia";
+}
+
+NavigatorUserMedia& NavigatorUserMedia::from(Navigator& navigator)
+{
+    NavigatorUserMedia* supplement = static_cast<NavigatorUserMedia*>(HeapSupplement<Navigator>::from(navigator, supplementName()));
+    if (!supplement) {
+        supplement = new NavigatorUserMedia();
+        provideTo(navigator, supplementName(), supplement);
+    }
+    return *supplement;
+}
+
+MediaDevices* NavigatorUserMedia::getMediaDevices()
+{
+    return m_mediaDevices;
+}
+
+MediaDevices* NavigatorUserMedia::mediaDevices(Navigator& navigator)
+{
+    return NavigatorUserMedia::from(navigator).getMediaDevices();
+}
+
+DEFINE_TRACE(NavigatorUserMedia)
+{
+    visitor->trace(m_mediaDevices);
+    HeapSupplement<Navigator>::trace(visitor);
+}
+
+} // namespace blink