Don't initialize ICU replacement character for UTF-32 encodings

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

 /*
  * Copyright (C) 2004, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov <ap@nypop.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 590 matching lines @@
 
 CString TextCodecICU::encodeInternal(const TextCodecInput& input,
                                      UnencodableHandling handling) {
   const UChar* source = input.begin();
   const UChar* end = input.end();
 
   UErrorCode err = U_ZERO_ERROR;
 
   switch (handling) {
     case QuestionMarksForUnencodables:
-      ucnv_setSubstChars(m_converterICU, "?", 1, &err);
+      // Non-byte-based encodings (i.e. UTF-16/32) don't need substitutions
+      // since they can encode any code point, and ucnv_setSubstChars would
+      // require a multi-byte substitution anyway.
+      if (!m_encoding.isNonByteBasedEncoding())
+        ucnv_setSubstChars(m_converterICU, "?", 1, &err);
 #if !defined(USING_SYSTEM_ICU)
       ucnv_setFromUCallBack(m_converterICU, UCNV_FROM_U_CALLBACK_SUBSTITUTE, 0,
                             0, 0, &err);
 #else
       ucnv_setFromUCallBack(
           m_converterICU, m_needsGBKFallbacks ? gbkCallbackSubstitute
                                               : UCNV_FROM_U_CALLBACK_SUBSTITUTE,
           0, 0, 0, &err);
 #endif
       break;
@@ skipping 76 matching lines @@
   return encodeCommon(characters, length, handling);
 }
 
 CString TextCodecICU::encode(const LChar* characters,
                              size_t length,
                              UnencodableHandling handling) {
   return encodeCommon(characters, length, handling);
 }
 
 }  // namespace WTF