Make a bunch of DocumentLoader functions private
https://bugs.webkit.org/show_bug.cgi?id=113601

Reviewed by Alexey Proskuryakov.

No new tests, cleanup only.

* loader/DocumentLoader.cpp:
* loader/DocumentLoader.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147336 268f45cc-cd09-0410-ab3c-d52691b4dbfc