SegmentedString: Use decrementAndCheckLength where possible

Source/platform/text/SegmentedString.h

 /*
     Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
 
     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
     version 2 of the License, or (at your option) any later version.
 
     This library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 201 matching lines @@
     };
 
     LookAheadResult lookAhead(const String& string) { return lookAheadInline(string, TextCaseSensitive); }
     LookAheadResult lookAheadIgnoringCase(const String& string) { return lookAheadInline(string, TextCaseInsensitive); }
 
     void advance()
     {
         if (m_fastPathFlags & Use8BitAdvance) {
             ASSERT(!m_pushedChar1);
             m_currentChar = m_currentString.incrementAndGetCurrentChar8();
-            m_currentString.decrementLength();
-            if (!m_currentString.haveOneCharacterLeft())
-                return;
-
-            updateSlowCaseFunctionPointers();
-
+            decrementAndCheckLength();
             return;
         }
 
         (this->*m_advanceFunc)();
     }
 
     inline void advanceAndUpdateLineNumber()
     {
         if (m_fastPathFlags & Use8BitAdvance) {
             ASSERT(!m_pushedChar1);
 
             bool haveNewLine = (m_currentChar == '\n') & !!(m_fastPathFlags & Use8BitAdvanceAndUpdateLineNumbers);
             m_currentChar = m_currentString.incrementAndGetCurrentChar8();
-            m_currentString.decrementLength();
-            bool haveOneCharacterLeft = m_currentString.haveOneCharacterLeft();
+            decrementAndCheckLength();
 
             if (haveNewLine) {

[tkent, 2015/08/27 03:08:01]

This block doesn't refer to data members updated by
updateSlowCaseFunctionPointers().  So, the change should be safe.

                 ++m_currentLine;
                 m_numberOfCharactersConsumedPriorToCurrentLine =  m_numberOfCharactersConsumedPriorToCurrentString + m_currentString.numberOfCharactersConsumed();
             }
 
-            if (haveOneCharacterLeft)
-                updateSlowCaseFunctionPointers();
-
             return;
         }
 
         (this->*m_advanceAndUpdateLineNumberFunc)();
     }
 
     void advanceAndASSERT(UChar expectedCharacter)
     {
         ASSERT_UNUSED(expectedCharacter, currentChar() == expectedCharacter);
         advance();
@@ skipping 155 matching lines @@
     bool m_closed;
     bool m_empty;
     unsigned char m_fastPathFlags;
     void (SegmentedString::*m_advanceFunc)();
     void (SegmentedString::*m_advanceAndUpdateLineNumberFunc)();
 };
 
 }
 
 #endif