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

third_party/WebKit/Source/core/html/parser/BackgroundHTMLInputStream.cpp

 /*
  * Copyright (C) 2013 Google, Inc. All Rights Reserved.
  *
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 72 matching lines @@
 
     bool isClosed = m_current.isClosed();
 
     m_current = checkpoint.input;
 
     for (size_t i = checkpoint.numberOfSegmentsAlreadyAppended; i < m_segments.size(); ++i) {
         ASSERT(!m_segments[i].isNull());
         m_current.append(SegmentedString(m_segments[i]));
     }
 
-    if (!unparsedInput.isEmpty())
-        m_current.prepend(SegmentedString(unparsedInput));
+    if (!unparsedInput.isEmpty()) {
+        m_current.prepend(SegmentedString(unparsedInput),
+            SegmentedString::PrependType::NewInput);
+    }
 
     if (isClosed && !m_current.isClosed())
         m_current.close();
 
     ASSERT(m_current.isClosed() == isClosed);
 
     m_segments.clear();
     m_checkpoints.clear();
     m_firstValidCheckpointIndex = 0;
     m_firstValidSegmentIndex = 0;
 
     updateTotalCheckpointTokenCount();
 }
 
 void BackgroundHTMLInputStream::updateTotalCheckpointTokenCount()
 {
     m_totalCheckpointTokenCount = 0;
     size_t lastCheckpointIndex = m_checkpoints.size();
     for (size_t i = 0; i < lastCheckpointIndex; ++i)
         m_totalCheckpointTokenCount += m_checkpoints[i].tokensExtractedSincePreviousCheckpoint;
 }
 
 } // namespace blink