Use messages for (some) public API errors

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 c98e6bc03d7f476857f514e92e19fc0e82f17588..7d4ed01d9b6dfaba797cc7014addba7da276d4a8 100644
--- a/pkg/front_end/lib/src/fasta/kernel/verifier.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/verifier.dart
@@ -24,13 +24,14 @@ import 'package:kernel/verifier.dart' show VerificationError, VerifyingVisitor;
 
 import '../deprecated_problems.dart' show deprecated_printUnexpected;
 
+import '../fasta_codes.dart';
+
 import 'redirecting_factory_body.dart' show RedirectingFactoryBody;
 
-List<VerificationError> verifyProgram(Program program,
-    {bool isOutline: false}) {
+List<LocatedMessage> verifyProgram(Program program, {bool isOutline: false}) {
   FastaVerifyingVisitor verifier = new FastaVerifyingVisitor(isOutline);
   program.accept(verifier);
-  return verifier.errors;
+  return verifier.errors.map(convertError).toList();
 }
 
 class FastaVerifyingVisitor extends VerifyingVisitor
@@ -106,3 +107,13 @@ class FastaVerifyingVisitor extends VerifyingVisitor
     problem(null, "Unexpected appearance of the unknown type.");
   }
 }
+
+LocatedMessage convertError(VerificationError error) {
+  var node = error.node ?? error.context;
+  int offset = node?.fileOffset ?? -1;
+  var file = node?.location?.file;
+  Uri uri = file == null ? null : Uri.parse(file);
+  return templateInternalVerificationError
+      .withArguments(error.details)
+      .withLocation(uri, offset);
+}