Mojo: Plumb "connection broken" out of RawChannel.

mojo/system/channel.cc

Index: mojo/system/channel.cc
diff --git a/mojo/system/channel.cc b/mojo/system/channel.cc
index bc912e8a8405fff1fc473857c9cfee4e3f21d1c8..2d78242f40827ab47b09317318261c22b377a0fb 100644
--- a/mojo/system/channel.cc
+++ b/mojo/system/channel.cc
@@ -296,6 +296,9 @@ void Channel::OnError(Error error) {
       // The other side was cleanly closed, so this isn't actually an error.
       DVLOG(1) << "RawChannel read error (shutdown)";
       break;
+    case ERROR_READ_BROKEN:
+      LOG(ERROR) << "RawChannel read error (connection broken)";
+      break;
     case ERROR_READ_BAD_MESSAGE:
       // Receiving a bad message means either a bug, data corruption, or
       // malicious attack (probably due to some other bug).