Remove struct HTMLTokenizer::Checkpoint which is never used

Source/core/html/parser/HTMLTokenizer.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2010 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
@@ skipping 103 matching lines @@
         DOCTYPESystemIdentifierDoubleQuotedState,
         DOCTYPESystemIdentifierSingleQuotedState,
         AfterDOCTYPESystemIdentifierState,
         BogusDOCTYPEState,
         CDATASectionState,
         // These CDATA states are not in the HTML5 spec, but we use them internally.
         CDATASectionRightSquareBracketState,
         CDATASectionDoubleRightSquareBracketState,
     };
 
-    struct Checkpoint {
-        STACK_ALLOCATED();
-        HTMLParserOptions options;
-        State state;
-        UChar additionalAllowedCharacter;
-        bool skipNextNewLine;
-        bool shouldAllowCDATA;
-
-        Checkpoint()
-            : options(0)
-            , state()
-            , additionalAllowedCharacter('\0')
-            , skipNextNewLine(false)
-            , shouldAllowCDATA(false)
-        {
-        }
-    };
-
     // This function returns true if it emits a token. Otherwise, callers
     // must provide the same (in progress) token on the next call (unless
     // they call reset() first).
     bool nextToken(SegmentedString&, HTMLToken&);
 
     // Returns a copy of any characters buffered internally by the tokenizer.
     // The tokenizer buffers characters when searching for the </script> token
     // that terminates a script element.
     String bufferedCharacters() const;
 
@@ skipping 127 matching lines @@
     // token (e.g., when lexing script). We buffer the name of the end tag
     // token here so we remember it next time we re-enter the tokenizer.
     Vector<LChar, 32> m_bufferedEndTagName;
 
     HTMLParserOptions m_options;
 };
 
 }
 
 #endif