code: func With(c context.Context, req *http.Request) context.Context {
  	return classicEnv.With(c, req)
  }
docs: // With adds various production GAE LUCI services to the context.
  //
  // Basically, it installs GAE-specific backends and caches for various
  // subsystems to make them work in GAE environment.
  //
  // One example is a backend for Logging: go.chromium.org/luci/common/logging.
  // Logs emitted through a With() context go to GAE logs.
  //
  // 'Production' here means the services will use real GAE APIs (not mocks or
  // stubs), so With should never be used from unit tests.