Turn DocumentParser::pinToMainThread into a cleaner api

Source/core/dom/DocumentParser.h

Index: Source/core/dom/DocumentParser.h
diff --git a/Source/core/dom/DocumentParser.h b/Source/core/dom/DocumentParser.h
index 1a075bf727c5280668936254836da852f9824119..2863cb73eb4b33c234f49164834758cd82d74c79 100644
--- a/Source/core/dom/DocumentParser.h
+++ b/Source/core/dom/DocumentParser.h
@@ -56,9 +56,6 @@ public:
     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.