I believe it was introduced by mistake here:
https://github.com/grpc/grpc/commit/3f1e69668642c42372b2e54c502458dc8dbba1bf

This addresses issue #752.

Since enums are themselves iterable there's no need to maintain a list
of the elements of the enum dating from back before the enum when its
values were just independent constants that hung out together.

This refactoring greatly reduces the base-internal use of packet kinds
and will make much simpler a future change distinguishing front-to-back
packet kinds from back-to-front packet kinds.

If for any reason, our definition of gpr_int64 is different from the definition of google::protobuf::int64, the virtual override would fail, as this needs to be of the precisely exactly the same type.
That change allows us to use protobuf's int64 definition.

Commit 31e65bea introduces a bug which causes starting server on a randomly
selected port.

Fix duplicated symbols caused by having definition instead of declaration in
header file.

deadline is passed by address to PyArg_ParseTuple to update its value.
However, deadline is a const double, so attempting to change its value
is undefined behavior. Remove the const to have well-defined behavior.

Previously client sends its own initiated stream ID in last-stream-id
field of GOAWAY, which misses the point in HTTP/2 specification.
Unless server push is utilized heavily, client should not assign its
transport's last_incoming_stream_id, since it is a response from
server to client's initiated stream ID.  This commit fixes it.

See GH-1024

Use this to relax the acq_loads in some fd_posix assertions. The primary
goal here is to avoid masking potential iomgr races from tsan.