Media Capabilities: add plumbing between Blink and media/blink/.

third_party/WebKit/public/platform/modules/media_capabilities/WebAudioConfiguration.h

+// Copyright 2017 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.
+
+#ifndef WebAudioConfiguration_h
+#define WebAudioConfiguration_h
+
+#include "base/optional.h"
+#include "public/platform/WebString.h"
+
+namespace blink {
+
+// Represents an AudioConfiguration dictionary to be used outside of Blink.
+// It is created by Blink and passed to consumers that can assume that all
+// required fields are properly set.
+struct WebAudioConfiguration {
+  WebString contentType;
+
+  // `channels` is Optional too but it will be reflected with `isNull()`.
+  WebString channels;
+  base::Optional<unsigned> bitrate;
+  base::Optional<unsigned> samplerate;
+};
+
+}  // namespace blink
+
+#endif  // WebAudioConfiguration_h