Move core MediaControls implementation to modules/media_controls/.

third_party/WebKit/Source/core/html/media/MediaControls.cpp

+// 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.
+
+#include "core/html/media/MediaControls.h"
+
+#include "core/html/HTMLMediaElement.h"
+
+namespace blink {
+
+MediaControls::MediaControls(HTMLMediaElement& mediaElement)
+    : m_mediaElement(&mediaElement) {}
+
+HTMLMediaElement& MediaControls::mediaElement() const {
+  return *m_mediaElement;
+}
+
+DEFINE_TRACE(MediaControls) {
+  visitor->trace(m_mediaElement);
+}
+
+}  // namespace blink