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

components/cast_channel/cast_channel_enum.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 COMPONENTS_CAST_CHANNEL_CAST_CHANNEL_ENUM_H_
+#define COMPONENTS_CAST_CHANNEL_CAST_CHANNEL_ENUM_H_
+
+#include <string>
+
+namespace cast_channel {
+
+// Maps to enum ReadyState in cast_channel.idl
+enum class ReadyState {
+  NONE,
+  CONNECTING,
+  OPEN,
+  CLOSING,
+  CLOSED,
+};
+
+// Maps to enum ChannelError in cast_channel.idl
+enum class ChannelError {
+  NONE,
+  CHANNEL_NOT_OPEN,
+  AUTHENTICATION_ERROR,
+  CONNECT_ERROR,
+  CAST_SOCKET_ERROR,
+  TRANSPORT_ERROR,
+  INVALID_MESSAGE,
+  INVALID_CHANNEL_ID,
+  CONNECT_TIMEOUT,
+  PING_TIMEOUT,
+  UNKNOWN,
+};
+
+// Maps to enum ChannelAuth in cast_channel.idl
+enum class ChannelAuthType {
+  NONE,
+  SSL_VERIFIED,
+};
+
+std::string ReadyStateToString(ReadyState ready_state);
+std::string ChannelErrorToString(ChannelError channel_error);
+std::string ChannelAuthTypeToString(ChannelAuthType channel_auth);
+
+}  // namespace cast_channel
+
+#endif  // COMPONENTS_CAST_CHANNEL_CAST_CHANNEL_ENUM_H_