XMLTreeViewer should be created only in the XML viewer mode
https://bugs.webkit.org/show_bug.cgi?id=119483

Reviewed by Alexey Proskuryakov.

XMLTreeViewer is created even for the XSL transform which is avoided by the patch.
The XMLTreeViewer::hasNoStyleInformation() is moved to XMLDocumentParserLibxml2.cpp
as static inline method as XMLTreeViewer should not have the responsibility for it.
Also removes an unnecessary conditional check while deciding for XML viewer mode.

Blink patch review links:
https://codereview.chromium.org/19552003/
https://codereview.chromium.org/22150003/

No new tests as the patch is about code refactoring.

* xml/XMLTreeViewer.cpp:
* xml/XMLTreeViewer.h:
* xml/parser/XMLDocumentParserLibxml2.cpp:
(WebCore::hasNoStyleInformation):
(WebCore::XMLDocumentParser::doEnd):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153707 268f45cc-cd09-0410-ab3c-d52691b4dbfc