[Qt][WK2] Add frame flattening setting to QWebPreferences.

[Qt][WK2] Add frame flattening setting to QWebPreferences.
https://bugs.webkit.org/show_bug.cgi?id=79099

Patch by Zalan Bujtas <zbujtas@gmail.com> on 2012-02-22
Reviewed by Simon Hausmann.

Frame flattening is enabled by default for Qt WebKit2.

* UIProcess/API/qt/qquickwebview.cpp:
(QQuickWebViewPrivate::initialize):
* UIProcess/API/qt/qwebpreferences.cpp:
(QWebPreferencesPrivate::testAttribute):
(QWebPreferencesPrivate::setAttribute):
(QWebPreferences::setNavigatorQtObjectEnabled):
(QWebPreferences::frameFlatteningEnabled):
(QWebPreferences::setFrameFlatteningEnabled):
* UIProcess/API/qt/qwebpreferences_p.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108471 268f45cc-cd09-0410-ab3c-d52691b4dbfc