Turn DocumentParser::pinToMainThread into a cleaner api

Source/core/dom/DocumentParser.h

 /*
  * Copyright (C) 2000 Peter Kelly (pmk@post.com)
  * Copyright (C) 2005, 2006 Apple Computer, Inc.
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  * Copyright (C) 2010 Google, Inc.
  *
  * 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.
@@ skipping 38 matching lines @@
     // insert is used by document.write.
     virtual void insert(const SegmentedString&) = 0;
 
     // The below functions are used by DocumentWriter (the loader).
     virtual void appendBytes(const char* bytes, size_t length) = 0;
     virtual bool needsDecoder() const { return false; }
     virtual void setDecoder(PassOwnPtr<TextResourceDecoder>);
     virtual TextResourceDecoder* decoder();
     virtual void setHasAppendedData() { }
 
-    // pinToMainThread also makes append() not yield before completion of that chunk.
-    virtual void pinToMainThread() { }
-
     // FIXME: append() should be private, but DocumentLoader::replaceDocumentWhileExecutingJavaScriptURL uses it for now.
     // FIXME: This really should take a PassOwnPtr to signify that it expects to take
     // ownership of the buffer. The parser expects the PassRefPtr to hold the only ref of the StringImpl.
     virtual void append(PassRefPtr<StringImpl>) = 0;
 
     virtual void finish() = 0;
 
     // FIXME: processingData() is only used by DocumentLoader::isLoadingInAPISense
     // and is very unclear as to what it actually means.  The LegacyHTMLDocumentParser
     // used to implement it.
@@ skipping 53 matching lines @@
     // Every DocumentParser needs a pointer back to the document.
     // m_document will be 0 after the parser is stopped.
     RawPtrWillBeMember<Document> m_document;
 
     WillBeHeapHashSet<RawPtrWillBeWeakMember<DocumentParserClient> > m_clients;
 };
 
 } // namespace blink
 
 #endif // DocumentParser_h