Drop Packets with the multipath bit set before decryption. Protected by FLAGS_quic_reloadable_flag_…

net/quic/core/quic_types.h

Index: net/quic/core/quic_types.h
diff --git a/net/quic/core/quic_types.h b/net/quic/core/quic_types.h
index 30fefd2137e69b831d471fcd4bab9c4c38eaebd3..d59ac6f51892e1bfb2b81726eaaa5fd22cf58899 100644
--- a/net/quic/core/quic_types.h
+++ b/net/quic/core/quic_types.h
@@ -184,6 +184,8 @@ enum QuicPacketPublicFlags {
   PACKET_PUBLIC_FLAGS_4BYTE_PACKET = PACKET_FLAGS_4BYTE_PACKET << 4,
   PACKET_PUBLIC_FLAGS_6BYTE_PACKET = PACKET_FLAGS_6BYTE_PACKET << 4,
 
+  // TODO(fayang): Remove PACKET_PUBLIC_FLAGS_MULTIPATH when deprecating
+  // gfe2_reloadable_flag_quic_remove_multipath_bit.
   // Bit 6: Does the packet header contain a path id?
   PACKET_PUBLIC_FLAGS_MULTIPATH = 1 << 6,
 
@@ -192,8 +194,14 @@ enum QuicPacketPublicFlags {
   // Bit 7: indicates the presence of a second flags byte.
   PACKET_PUBLIC_FLAGS_TWO_OR_MORE_BYTES = 1 << 7,
 
+  // TODO(fayang): Remove PACKET_PUBLIC_FLAGS_MAX and rename
+  // PACKET_PUBLIC_FLAGS_MAX_WITHOUT_MULTIPATH_FLAG when deprecating
+  // gfe2_reloadable_flag_quic_remove_multipath_bit.
   // All bits set (bit 7 is not currently used): 01111111
   PACKET_PUBLIC_FLAGS_MAX = (1 << 7) - 1,
+
+  // All bits set (bits 6 and 7 are not currently used): 00111111
+  PACKET_PUBLIC_FLAGS_MAX_WITHOUT_MULTIPATH_FLAG = (1 << 6) - 1,
 };
 
 // The private flags are specified in one byte.