Mark analysis_server as being strong-mode clean

pkg/analysis_server/lib/src/channel/byte_stream_channel.dart

Index: pkg/analysis_server/lib/src/channel/byte_stream_channel.dart
diff --git a/pkg/analysis_server/lib/src/channel/byte_stream_channel.dart b/pkg/analysis_server/lib/src/channel/byte_stream_channel.dart
index ce6235d01bfb3f5716b4266c96ebd0b88834002e..c17b77b748fbee5abe39aae81751d8feb7ec33e3 100644
--- a/pkg/analysis_server/lib/src/channel/byte_stream_channel.dart
+++ b/pkg/analysis_server/lib/src/channel/byte_stream_channel.dart
@@ -51,10 +51,11 @@ class ByteStreamClientChannel implements ClientCommunicationChannel {
   }
 
   @override
-  Future<Response> sendRequest(Request request) {
+  Future<Response> sendRequest(Request request) async {
     String id = request.id;
     output.write(JSON.encode(request.toJson()) + '\n');
-    return responseStream.firstWhere((Response response) => response.id == id);
+    return await responseStream
+        .firstWhere((Response response) => response.id == id);
   }
 }