[cast_channel] Make cast_channel related files not depend on "cast_channel.h"

extensions/browser/api/cast_channel/cast_channel_enum_util.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 EXTENSIONS_BROWSER_API_CAST_CHANNEL_CAST_CHANNEL_TYPE_UTIL_H_
+#define EXTENSIONS_BROWSER_API_CAST_CHANNEL_CAST_CHANNEL_TYPE_UTIL_H_
+
+#include "components/cast_channel/cast_channel_enum.h"
+#include "extensions/common/api/cast_channel.h"
+
+namespace extensions {
+namespace api {
+namespace cast_channel {
+
+api::cast_channel::ReadyState ToReadyState(
+    ::cast_channel::ReadyState ready_state);
+api::cast_channel::ChannelError ToChannelError(
+    ::cast_channel::ChannelError channel_error);
+api::cast_channel::ChannelAuthType ToChannelAuthType(
+    ::cast_channel::ChannelAuthType channel_auth);
+::cast_channel::ChannelAuthType ToChannelAuthTypeInternal(
+    api::cast_channel::ChannelAuthType channel_auth);
+
+}  // namespace cast_channel
+}  // namespace api
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_API_CAST_CHANNEL_CAST_CHANNEL_TYPE_UTIL_H_