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

extensions/browser/api/cast_channel/keep_alive_delegate.cc

Index: extensions/browser/api/cast_channel/keep_alive_delegate.cc
diff --git a/extensions/browser/api/cast_channel/keep_alive_delegate.cc b/extensions/browser/api/cast_channel/keep_alive_delegate.cc
index 71adb89bf354497954bdca9797826654bf19b25a..58a0658df388d7bfc9d57264a31feeba72b2caf4 100644
--- a/extensions/browser/api/cast_channel/keep_alive_delegate.cc
+++ b/extensions/browser/api/cast_channel/keep_alive_delegate.cc
@@ -48,6 +48,8 @@ const char KeepAliveDelegate::kHeartbeatPingType[] = "PING";
 // static
 const char KeepAliveDelegate::kHeartbeatPongType[] = "PONG";
 
+using ::cast_channel::ChannelError;
+
 // static
 CastMessage KeepAliveDelegate::CreateKeepAliveMessage(
     const char* message_type) {
@@ -146,19 +148,19 @@ void KeepAliveDelegate::SendKeepAliveMessageComplete(const char* message_type,
     // An error occurred while sending the ping response.
     VLOG(1) << "Error sending " << message_type;
     logger_->LogSocketEventWithRv(socket_->id(), proto::PING_WRITE_ERROR, rv);
-    OnError(cast_channel::CHANNEL_ERROR_SOCKET_ERROR);
+    OnError(ChannelError::SOCKET_ERROR);
   }
 }
 
 void KeepAliveDelegate::LivenessTimeout() {
-  OnError(cast_channel::CHANNEL_ERROR_PING_TIMEOUT);
+  OnError(ChannelError::PING_TIMEOUT);
   Stop();
 }
 
 // CastTransport::Delegate interface.
 void KeepAliveDelegate::OnError(ChannelError error_state) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  VLOG(1) << "KeepAlive::OnError: " << error_state;
+  VLOG(1) << "KeepAlive::OnError: " << ::cast_channel::ToString(error_state);
   inner_delegate_->OnError(error_state);
   Stop();
 }