Instead of passing the transport byte counts back up through the filter
stack to be reported to the `CallTracer`, we now have the transport
pass the transport byte counts directly to the `CallTracer` itself.
This will eventually allow us to avoid unnecessarily storing these byte
counts in cases where no `CallTracer` actually cares about the data, which
will reduce per-call memory. (In the short term, it actually increases
memory usage, but we can separately do some work to avoid the memory
usage in the transport by removing the `grpc_transport_stream_stats`
struct from the legacy filter API.)
This is a prereq for supporting `CallTracer` in the new call v3 stack,
which does not include the transport byte counts as part of the
receieve-trailing-metadata hook, unlike the legacy filter stack.
This change is controlled by the `call_tracer_in_transport` experiment,
which is enabled by default.
As part of this experiment, we also fix a couple of related bugs:
- On the client side, the chttp2 transport was incorrectly adding
annotations to the parent `ClientCallTracer` instead of the
`CallAttemptTracer`.
- The OpenCensus `ServerCallTracer` was incorrectly swapping the values
of sent and received bytes.
PiperOrigin-RevId: 650728181
Mark D. Roth