Use nonBlocking stdio for LSP

Change-Id: I20f7ed183d08b7fc778b4cb643eff6f82c9f3f48
Reviewed-on: https://dart-review.googlesource.com/c/90001
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Danny Tuppeny <dantup@google.com>
diff --git a/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart b/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart
index 1b5cde5..92fd980 100644
--- a/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart
+++ b/pkg/analysis_server/lib/src/server/lsp_stdio_server.dart
@@ -33,7 +33,7 @@
    */
   Future serveStdio() {
     LspByteStreamServerChannel serverChannel = new LspByteStreamServerChannel(
-        stdin, stdout, socketServer.instrumentationService);
+        stdin, stdout.nonBlocking, socketServer.instrumentationService);
     socketServer.createAnalysisServer(serverChannel);
     return serverChannel.closed;
   }