Code completion bug fix, don't suggest optional field formal parameters that are already in the con…

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

Index: pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
index 43514fb64d8f1928f229529ffd3973ba7b411da2..62bda0c5dd23abceb3241efb4a460354cc5fe0aa 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
@@ -36,6 +36,10 @@ class FieldFormalContributor extends DartCompletionContributor {
     // Compute the list of fields already referenced in the constructor
     List<String> referencedFields = new List<String>();
     for (FormalParameter param in constructorDecl.parameters.parameters) {
+      if (param is DefaultFormalParameter &&
+          param.parameter is FieldFormalParameter) {
+        param = (param as DefaultFormalParameter).parameter;
+      }
       if (param is FieldFormalParameter) {
         SimpleIdentifier fieldId = param.identifier;
         if (fieldId != null && fieldId != request.target.entity) {