Implement enumerateDevices() according to spec.

Source/modules/mediastream/MediaDevices.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/MediaDevices.h"
+
+#include "bindings/core/v8/ScriptPromise.h"
+#include "bindings/core/v8/ScriptPromiseResolver.h"
+#include "bindings/core/v8/ScriptState.h"
+#include "core/dom/DOMException.h"
+#include "core/dom/Document.h"
+#include "core/dom/ExceptionCode.h"
+#include "modules/mediastream/UserMediaController.h"
+
+namespace blink {
+
+ScriptPromise MediaDevices::enumerateDevices(ScriptState* scriptState)
+{
+    Document* document = toDocument(scriptState->executionContext());
+    UserMediaController* userMedia = UserMediaController::from(document->frame());
+    if (!userMedia)
+        return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(NotSupportedError, "No media device controller available; is this a detached window?"));
+
+    MediaDevicesRequest* request = MediaDevicesRequest::create(scriptState, userMedia);
+    return request->start();
+}
+
+} // namespace blink