Deprecate all diagnostics methods that use strings.

pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart b/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
index 94ab897e1293acb409e71db71295ad6daad4a107..0e08d04f00704ae7742edbceb93056da2c0bf4f9 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
-import 'package:front_end/src/fasta/errors.dart';
+import 'package:front_end/src/fasta/deprecated_problems.dart';
 import 'package:front_end/src/fasta/type_inference/type_inferrer.dart';
 import 'package:kernel/ast.dart';
 
@@ -217,7 +217,7 @@ abstract class TypePromoterImpl extends TypePromoter {
   void finished() {
     debugEvent('finished');
     if (_currentScope is! _TopLevelScope) {
-      internalError('Stack not empty');
+      deprecated_internalProblem('Stack not empty');
     }
   }