internal/lsp: restore the rpc metrics

The special handler was dropped in cl/191963 which moved the logging functionality, but
was still needed for the rpc metrics

Change-Id: I494ef47646fe0d705709694378dbc981b549622a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/205164
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/cmd/serve.go

diff --git a/internal/lsp/cmd/serve.go b/internal/lsp/cmd/serve.go
index ceca1f1..79b4546 100644
--- a/internal/lsp/cmd/serve.go
+++ b/internal/lsp/cmd/serve.go
@@ -81,10 +81,11 @@
 		return s.forward()
 	}
 
-	// For debugging purposes only.
-	run := func(ctx context.Context, srv *lsp.Server) {
-		go srv.Run(ctx)
+	prepare := func(ctx context.Context, srv *lsp.Server) *lsp.Server {
+		srv.Conn.AddHandler(&handler{})
+		return srv
 	}
+	run := func(ctx context.Context, srv *lsp.Server) { go prepare(ctx, srv).Run(ctx) }
 	if s.Address != "" {
 		return lsp.RunServerOnAddress(ctx, s.app.cache, s.Address, run)
 	}
@@ -96,7 +97,7 @@
 		stream = protocol.LoggingStream(stream, out)
 	}
 	ctx, srv := lsp.NewServer(ctx, s.app.cache, stream)
-	return srv.Run(ctx)
+	return prepare(ctx, srv).Run(ctx)
 }
 
 func (s *Serve) forward() error {
@@ -119,9 +120,7 @@
 	return <-errc
 }
 
-type handler struct {
-	out io.Writer
-}
+type handler struct{}
 
 type rpcStats struct {
 	method     string