Deprecate all diagnostics methods that use strings.

pkg/front_end/lib/src/fasta/parser/token_stream_rewriter.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:front_end/src/fasta/errors.dart';
+import 'package:front_end/src/fasta/deprecated_problems.dart';
 import 'package:front_end/src/scanner/token.dart' show BeginToken, Token;
 
 /// Provides the capability of inserting tokens into a token stream by rewriting
 /// the previous token to point to the inserted token.
 ///
 /// This class has been designed to take advantage of "previousToken" pointers
 /// when they are present, but not to depend on them.  When they are not
 /// present, it uses heuristics to try to find the find the previous token as
 /// quickly as possible by walking through tokens starting at the start of the
 /// file.
@@ skipping 50 matching lines @@
     // if it makes sense to do so.
     if (_lastPreviousToken != null &&
         target.charOffset >= _lastPreviousToken.charOffset) {
       Token previous = _scanForPreviousToken(target, _lastPreviousToken);
       if (previous != null) return previous;
     }
 
     // Otherwise scan forward from the start of the token stream.
     Token previous = _scanForPreviousToken(target, _head);
     if (previous == null) {
-      internalError('Could not find previous token');
+      deprecated_internalProblem('Could not find previous token');
     }
     return previous;
   }
 
   /// Searches for the token that immediately precedes [target], using [pos] as
   /// a starting point.
   ///
   /// Uses heuristics to skip matching `{}`, `[]`, `()`, and `<>` if possible.
   ///
   /// If no such token is found, returns `null`.
   Token _scanForPreviousToken(Token target, Token pos) {
     while (!identical(pos.next, target)) {
       Token nextPos;
       if (pos is BeginToken &&
           pos.endGroup != null &&
           pos.endGroup.charOffset < target.charOffset) {
         nextPos = pos.endGroup;
       } else {
         nextPos = pos.next;
         if (nextPos == null || nextPos.charOffset > target.charOffset) {
           return null;
         }
       }
       pos = nextPos;
     }
     return pos;
   }
 }