Add typedef AST node boilerplate.

pkg/front_end/lib/src/fasta/kernel/verifier.dart

Index: pkg/front_end/lib/src/fasta/kernel/verifier.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/verifier.dart b/pkg/front_end/lib/src/fasta/kernel/verifier.dart
index 6d77e8489f09c133d28f42f3c8b74c9c2eff355c..91b691a8925c7732cdb76844cdb216afcbfa0de5 100644
--- a/pkg/front_end/lib/src/fasta/kernel/verifier.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/verifier.dart
@@ -44,7 +44,8 @@ class FastaVerifyingVisitor extends VerifyingVisitor
   }
 
   @override
-  problem(TreeNode node, String details) {
+  problem(TreeNode node, String details, {TreeNode context}) {
+    context ??= this.context;
     VerificationError error = new VerificationError(context, node, details);
     printUnexpected(Uri.parse(fileUri), node?.fileOffset ?? -1, "$error");
     errors.add(error);