Remove implicit conversions from scoped_refptr to T* in mojo/

mojo/system/proxy_message_pipe_endpoint.cc

Index: mojo/system/proxy_message_pipe_endpoint.cc
diff --git a/mojo/system/proxy_message_pipe_endpoint.cc b/mojo/system/proxy_message_pipe_endpoint.cc
index 79074d0222c52f046fb17702637d061f17672e27..81adda545052764e760da686d0ba0c75ed3da44a 100644
--- a/mojo/system/proxy_message_pipe_endpoint.cc
+++ b/mojo/system/proxy_message_pipe_endpoint.cc
@@ -83,7 +83,7 @@ void ProxyMessagePipeEndpoint::EnqueueMessage(
 
 void ProxyMessagePipeEndpoint::Attach(scoped_refptr<Channel> channel,
                                       MessageInTransit::EndpointId local_id) {
-  DCHECK(channel);
+  DCHECK(channel.get());
   DCHECK_NE(local_id, MessageInTransit::kInvalidEndpointId);
 
   DCHECK(!is_attached());