Only populate line number in case parsing synchronously.

Source/core/html/parser/HTMLDocumentParser.h

 /*
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 66 matching lines @@
     virtual void trace(Visitor*) override;
 
     // Exposed for HTMLParserScheduler
     void resumeParsingAfterYield();
 
     static void parseDocumentFragment(const String&, DocumentFragment*, Element* contextElement, ParserContentPolicy = AllowScriptingContent);
 
     HTMLTokenizer* tokenizer() const { return m_tokenizer.get(); }
 
     virtual TextPosition textPosition() const override final;
+    virtual bool isParsingAtLineNumber() const override final;
     virtual OrdinalNumber lineNumber() const override final;
 
     virtual void suspendScheduledTasks() override final;
     virtual void resumeScheduledTasks() override final;
 
     struct ParsedChunk {
         OwnPtr<CompactHTMLTokenStream> tokens;
         PreloadRequestStream preloads;
         XSSInfoStream xssInfos;
         HTMLTokenizer::State tokenizerState;
@@ skipping 99 matching lines @@
     WeakPtrFactory<HTMLDocumentParser> m_weakFactory;
     WeakPtr<BackgroundHTMLParser> m_backgroundParser;
     OwnPtrWillBeMember<HTMLResourcePreloader> m_preloader;
 
     bool m_shouldUseThreading;
     bool m_endWasDelayed;
     bool m_haveBackgroundParser;
     bool m_tasksWereSuspended;
     unsigned m_pumpSessionNestingLevel;
     unsigned m_pumpSpeculationsSessionNestingLevel;
+    bool m_isParsingAtLineNumber;
 };
 
 }
 
 #endif