Remove PathCloseFrame, QuicPathId, DefaultPathId and InvalidPathId.

net/quic/core/quic_connection.cc

Index: net/quic/core/quic_connection.cc
diff --git a/net/quic/core/quic_connection.cc b/net/quic/core/quic_connection.cc
index 6d0c4e7446d0890776d65a6cac3304c459b93937..97e689db789b1217475b57031258f32570ed09dc 100644
--- a/net/quic/core/quic_connection.cc
+++ b/net/quic/core/quic_connection.cc
@@ -904,16 +904,6 @@ bool QuicConnection::OnBlockedFrame(const QuicBlockedFrame& frame) {
   return connected_;
 }
 
-bool QuicConnection::OnPathCloseFrame(const QuicPathCloseFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPathCloseFrame(frame);
-  }
-  QUIC_DLOG(INFO) << ENDPOINT
-                  << "PATH_CLOSE_FRAME received for path: " << frame.path_id;
-  return connected_;
-}
-
 void QuicConnection::OnPacketComplete() {
   // Don't do anything if this packet closed the connection.
   if (!connected_) {