SegmentedString::prepend should know if the prepended string is new or previously consumed

third_party/WebKit/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 193 matching lines @@
     {
         if (m_currentString.length())
             m_currentChar = m_currentString.getCurrentChar();
         updateAdvanceFunctionPointers();
     }
 
     void clear();
     void close();
 
     void append(const SegmentedString&);
-    void prepend(const SegmentedString&);
+    enum class PrependType {
+        NewInput = 0,
+        Unconsume = 1,
+    };
+    void prepend(const SegmentedString&, PrependType);
 
     bool excludeLineNumbers() const { return m_currentString.excludeLineNumbers(); }
     void setExcludeLineNumbers();
 
     void push(UChar);
 
     bool isEmpty() const { return m_empty; }
     unsigned length() const;
 
     bool isClosed() const { return m_closed; }
@@ skipping 91 matching lines @@
     void setCurrentPosition(OrdinalNumber line, OrdinalNumber columnAftreProlog, int prologLength);
 
 private:
     enum FastPathFlags {
         NoFastPath = 0,
         Use8BitAdvanceAndUpdateLineNumbers = 1 << 0,
         Use8BitAdvance = 1 << 1,
     };
 
     void append(const SegmentedSubstring&);
-    void prepend(const SegmentedSubstring&);
+    void prepend(const SegmentedSubstring&, PrependType);
 
     void advance8();
     void advance16();
     void advanceAndUpdateLineNumber8();
     void advanceAndUpdateLineNumber16();
     void advanceSlowCase();
     void advanceAndUpdateLineNumberSlowCase();
     void advanceEmpty();
     void advanceSubstring();
 
@@ skipping 55 matching lines @@
     {
         unsigned count = string.length();
         if (count > length())
             return NotEnoughCharacters;
         UChar* consumedCharacters;
         String consumedString = String::createUninitialized(count, consumedCharacters);
         advance(count, consumedCharacters);
         LookAheadResult result = DidNotMatch;
         if (consumedString.startsWith(string, caseSensitivity))
             result = DidMatch;
-        prepend(SegmentedString(consumedString));
+        prepend(SegmentedString(consumedString), PrependType::Unconsume);
         return result;
     }
 
     bool isComposite() const { return !m_substrings.isEmpty(); }
 
     SegmentedSubstring m_currentString;
     UChar m_currentChar;
     int m_numberOfCharactersConsumedPriorToCurrentString;
     int m_numberOfCharactersConsumedPriorToCurrentLine;
     int m_currentLine;
     Deque<SegmentedSubstring> m_substrings;
     bool m_closed;
     bool m_empty;
     unsigned char m_fastPathFlags;
     void (SegmentedString::*m_advanceFunc)();
     void (SegmentedString::*m_advanceAndUpdateLineNumberFunc)();
 };
 
 } // namespace blink
 
 #endif