Fix tests broken by r44880.

pkg/analyzer/lib/src/generated/ast.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.ast;
 
 import 'dart:collection';
@@ skipping 16712 matching lines @@
         isMultiline = false;
         start++;
       } else if (start < lexeme.length && lexeme.codeUnitAt(start) == 0x22) {
         isSingleQuoted = false;
         isMultiline = false;
         start++;
       }
     }
     end = lexeme.length;
     if (isLast) {
-      if (StringUtilities.endsWith3(lexeme, 0x22, 0x22, 0x22) ||
-          StringUtilities.endsWith3(lexeme, 0x27, 0x27, 0x27)) {
+      if (start + 3 <= end &&
+          (StringUtilities.endsWith3(lexeme, 0x22, 0x22, 0x22) ||
+              StringUtilities.endsWith3(lexeme, 0x27, 0x27, 0x27))) {
         end -= 3;
-      } else if (StringUtilities.endsWithChar(lexeme, 0x22) ||
-          StringUtilities.endsWithChar(lexeme, 0x27)) {
+      } else if (start + 1 <= end &&
+          (StringUtilities.endsWithChar(lexeme, 0x22) ||
+              StringUtilities.endsWithChar(lexeme, 0x27))) {
         end -= 1;
       }
     }
   }
 
   /**
    * Given the [lexeme] for a multi-line string whose content begins at the
    * given [start] index, return the index of the first character that is
    * included in the value of the string. According to the specification:
    *
@@ skipping 3402 matching lines @@
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitYieldStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     _safelyVisitChild(_expression, visitor);
   }
 }