Initial support for the NNBD proposal

pkg/analyzer/lib/src/dart/ast/utilities.dart

Index: pkg/analyzer/lib/src/dart/ast/utilities.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/utilities.dart b/pkg/analyzer/lib/src/dart/ast/utilities.dart
index cbabff9b4f31c67932abfe4f6aebdc234ddc1fb8..6c792c873c6ad0935a07fecc8eeb563be543a0c4 100644
--- a/pkg/analyzer/lib/src/dart/ast/utilities.dart
+++ b/pkg/analyzer/lib/src/dart/ast/utilities.dart
@@ -7203,6 +7203,9 @@ class ToSourceVisitor implements AstVisitor<Object> {
     _visitNode(node.identifier);
     _visitNode(node.typeParameters);
     _visitNode(node.parameters);
+    if (node.question != null) {
+      _writer.print('?');
+    }
     return null;
   }
 
@@ -7649,6 +7652,9 @@ class ToSourceVisitor implements AstVisitor<Object> {
   Object visitTypeName(TypeName node) {
     _visitNode(node.name);
     _visitNode(node.typeArguments);
+    if (node.question != null) {
+      _writer.print('?');
+    }
     return null;
   }