Move MediaStreamTrack contentHint to separate IDL.

third_party/WebKit/Source/modules/mediastream/MediaStreamTrackContentHint.h

+// Copyright 2016 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 MediaStreamTrackContentHint_h
+#define MediaStreamTrackContentHint_h
+
+#include "modules/mediastream/MediaStreamTrack.h"
+
+namespace blink {
+
+class MediaStreamTrackContentHint final {
+ public:
+  static String contentHint(const MediaStreamTrack& track) {
+    return track.contentHint();
+  }
+  static void setContentHint(MediaStreamTrack& track, const String& hint) {
+    track.setContentHint(hint);
+  }
+};
+
+}  // namespace blink
+
+#endif  // MediaStreamTrack_h