[WK2] Make WebPageProxy use deviceScaleFactor() in creationParameters().
https://bugs.webkit.org/show_bug.cgi?id=110218

Reviewed by Darin Adler.

Make the WebPageProxy::creationParameters use the accessor
deviceScaleFactor() instead of using m_intrinsicDeviceScaleFactor
directly. This will restore the custom device scale factor when
reattaching to the WebProcess after a crash.

Moreover, it will enable the Qt and ELF ports to use the
existing C API for overriding the device scale factor instead
of using the WebPageProxy directly or adding new C API to set
the intrinsic device scale factor.

* UIProcess/API/efl/EwkView.cpp:
(EwkView::setDeviceScaleFactor):
* UIProcess/API/qt/qquickwebpage.cpp:
(QQuickWebPage::updatePaintNode):
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::creationParameters):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150063 268f45cc-cd09-0410-ab3c-d52691b4dbfc