This is in preparation for preventing any user-supplied metadata starting with "grpc-", which is reserved.
* stats: add methods to allow setting grpc-trace-bin and grpc-tags-bin headers
Pick these up in grpc's transport when sending and fill them when receiving.
* Add tags/trace to metadata and tests for that behavior
This is temporary to maintain compatibility and provide a migration strategy.
When an error implemented by the status package is returned from a service
handler, the server will transmit a rich status message in the
"grpc-status-details-bin" trailing metadata field if any detailed data is
attached to the error. Client-side, we will decode them if present in the
server's response and return them to the user code performing the RPC.
This is backward compatible with the existing errors supported by the grpc
package. However, the grpc.Errorf, grpc.Code and grpc.ErrorDesc functions for
managing errors are now deprecated; status.Errorf and status.Status type
asserions should be used instead.
* add stats.tagger APIs and connection stats.
* fix comments
use ac.ctx in http2client
change name and comments
small fixes stats_tests
* add a TODO to ConnTagInfo
* rename handle to handleRPC
* modify stats comments