Re-add GRPC_ARG_MAX_MESSAGE_LENGTH, which can't be removed yet.

doc/core/pending_api_cleanups.md

@@ -11,4 +11,7 @@ This file lists all pending backward-compatibility changes that should
 be cleaned up the next time we are going to bump the major version
 number:
 
-(none currently)
+- remove `GRPC_ARG_MAX_MESSAGE_LENGTH` channel arg from
+  `include/grpc/impl/codegen/grpc_types.h` (commit `af00d8b`)
+  (cannot be done until after next grpc release, so that TensorFlow can
+  use the same code both internally and externally)

include/grpc/impl/codegen/grpc_types.h

@@ -151,6 +151,8 @@ typedef struct {
 /** Maximum message length that the channel can receive. Int valued, bytes.
     -1 means unlimited. */
 #define GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH "grpc.max_receive_message_length"
+/** \deprecated For backward compatibility. */
+#define GRPC_ARG_MAX_MESSAGE_LENGTH GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH
 /** Maximum message length that the channel can send. Int valued, bytes.
     -1 means unlimited. */
 #define GRPC_ARG_MAX_SEND_MESSAGE_LENGTH "grpc.max_send_message_length"