Issue 27856. Fix for reponding to execution domain requests.

pkg/analysis_server/lib/src/domain_completion.dart

Index: pkg/analysis_server/lib/src/domain_completion.dart
diff --git a/pkg/analysis_server/lib/src/domain_completion.dart b/pkg/analysis_server/lib/src/domain_completion.dart
index c0df56e96294b4e1a304e1b9fdc1d504894ce206..6bad4431a2ab122d8773b9cdd4259df474e243cb 100644
--- a/pkg/analysis_server/lib/src/domain_completion.dart
+++ b/pkg/analysis_server/lib/src/domain_completion.dart
@@ -107,14 +107,11 @@ class CompletionDomainHandler implements RequestHandler {
     if (server.searchEngine == null) {
       return new Response.noIndexGenerated(request);
     }
-    runZoned(() {
-      try {
-        String requestName = request.method;
-        if (requestName == COMPLETION_GET_SUGGESTIONS) {
-          processRequest(request);
-        }
-      } on RequestFailure catch (exception) {
-        return exception.response;
+    return runZoned(() {
+      String requestName = request.method;
+      if (requestName == COMPLETION_GET_SUGGESTIONS) {
+        processRequest(request);
+        return Response.DELAYED_RESPONSE;
       }
       return null;
     }, onError: (exception, stackTrace) {
@@ -123,7 +120,6 @@ class CompletionDomainHandler implements RequestHandler {
           exception,
           stackTrace);
     });
-    return Response.DELAYED_RESPONSE;
   }
 
   /**