Wean BackgroundHTMLParser off HTMLInputStream
https://bugs.webkit.org/show_bug.cgi?id=107575

Reviewed by Eric Seidel.

The BackgroundHTMLParser doesn't need to use HTMLInputStream because it
doesn't need to handle nested calls to document.write. Instead, we can
just use a SegmentedString directly, which will let us checkpoint
m_input for speculation.

* html/parser/BackgroundHTMLParser.cpp:
(WebCore::BackgroundHTMLParser::append):
(WebCore::BackgroundHTMLParser::finish):
(WebCore::BackgroundHTMLParser::markEndOfFile):
(WebCore):
(WebCore::BackgroundHTMLParser::pumpTokenizer):
* html/parser/BackgroundHTMLParser.h:
(BackgroundHTMLParser):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140446 268f45cc-cd09-0410-ab3c-d52691b4dbfc