anchor.diff:        Expression expression = (entity as ExpressionStatement).expression;
         if (expression is SimpleIdentifier) {
           Token token = expression.token;
  -        Token previous = token.previous;
  +        Token previous = node.findPrevious(token);
           if (previous.isSynthetic) {
  -          previous = previous.previous;
  +          previous = node.findPrevious(previous);
           }
           Token next = token.next;
           if (next.isSynthetic) {
  
positive.code:   static bool _isPreviousTokenSynthetic(Object entity, TokenType type) {
      if (entity is AstNode) {
        Token token = entity.beginToken;
        Token previousToken = token.previous;
        return previousToken.isSynthetic && previousToken.type == type;
      }
      return false;
  
negative.code:     }
      if (entity == node.rightParenthesis) {
        _addExpressionKeywords(node);
        Token previous = node.findPrevious(entity as Token);
        if (previous.isSynthetic) {
          previous = node.findPrevious(previous);
        }
        if (previous.lexeme == ')') {
          _addSuggestion(Keyword.ASYNC);
  