Avoid infinite recursion in StringImpl::asciiForDebugging

third_party/WebKit/Source/wtf/text/StringImpl.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller ( mueller@kde.org )
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2013 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2006 Andrew Wellington (proton@wiretapped.net)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 317 matching lines @@
   // will try to remove them from the wrong AtomicStringTable.
   if (isAtomic())
     return false;
   if (hasOneRef())
     return true;
   return false;
 }
 
 #if DCHECK_IS_ON()
 std::string StringImpl::asciiForDebugging() const {
-  CString ascii = String(substring(0, 128)).ascii();
+  CString ascii = String(isolatedCopy()->substring(0, 128)).ascii();
   return std::string(ascii.data(), ascii.length());
 }
 #endif
 
 PassRefPtr<StringImpl> StringImpl::createUninitialized(unsigned length,
                                                        LChar*& data) {
   if (!length) {
     data = 0;
     return empty();
   }
@@ skipping 1847 matching lines @@
     } else if (localeIdMatchesLang(localeIdentifier, "lt")) {
       // TODO(rob.buis) implement upper-casing rules for lt
       // like in StringImpl::upper(locale).
     }
   }
 
   return toUpper(c);
 }
 
 }  // namespace WTF