Prioritize required name param completions (flutter-intellij#1049).

pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart

Index: pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
index 92ed30109e5866d3bc8dcc01c4ae2384fdb26157..12e58eec3b4a53bed4d5f16160821d926ba38a5d 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
@@ -254,9 +254,14 @@ class ArgListContributor extends DartCompletionContributor {
       if (appendComma) {
         completion += ',';
       }
+
+      final int relevance = parameter.isRequired
+          ? DART_RELEVANCE_NAMED_PARAMETER_REQUIRED
+          : DART_RELEVANCE_NAMED_PARAMETER;
+
       CompletionSuggestion suggestion = new CompletionSuggestion(
           CompletionSuggestionKind.NAMED_ARGUMENT,
-          DART_RELEVANCE_NAMED_PARAMETER,
+          relevance,
           completion,
           selectionOffset,
           0,