[mwitkow]

There's actually a stand-alone proxy that translates the REST mappings of `google.api.http` into gRPC requests. It relies on code-generation: https://github.com/grpc-ecosystem/grpc-gateway

This has been the way we've been shipping our REST services until now, but the need to recompile the proxy was a major hinderence to our development speed. Hence gRPC-Web implementation.