Make StringImpl's content immutable

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
  * License as published by the Free Software Foundation; either
@@ skipping 664 matching lines @@
 static PassRefPtr<StringImpl> caseConvert(const UChar* source16, size_t length, icuCaseConverter converter, const char* locale, StringImpl* originalString)
 {
     UChar* data16;
     size_t targetLength = length;
     RefPtr<StringImpl> output = StringImpl::createUninitialized(length, data16);
     do {
         UErrorCode status = U_ZERO_ERROR;
         targetLength = converter(data16, targetLength, source16, length, locale, &status);
         if (U_SUCCESS(status)) {
             if (length > 0)
-                output->truncateAssumingIsolated(targetLength);
+                return output->substring(0, targetLength);
             return output.release();
         }
         if (status != U_BUFFER_OVERFLOW_ERROR)
             return originalString;
         // Expand the buffer.
         output = StringImpl::createUninitialized(targetLength, data16);
     } while (true);
 }
 
 PassRefPtr<StringImpl> StringImpl::lower(const AtomicString& localeIdentifier)
@@ skipping 1413 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