Provide a hook for metadata providers that need to generate their
metadata for each RPC. An example is authorization, where the provider
may need to refresh a token before it can provide the header.
Add stackdriver logging examplei to demonstrate calling a Google API.
Updated other examples to protobuf 0.6.0 (protoc plugin 0.7.8).
Updated SDK requirement to Dart 1.24.3, which adds support for creating a SecurityContext that trusts built-in roots, and support for ALPN on macOS.
Picks up fix for sending endStream bit on the requested frame, instead
of on an empty data frame following it.
Needed for interoperability with the Go gRPC client, since it otherwise
failed to recognize the trailer frame sent from the server.
Fixes#13.
Alexandre Ardhuin
Jon Kirkman
Jakob Andersen