Incorrect UA style when printing a simple document

Incorrect UA style when printing a simple document
https://bugs.webkit.org/show_bug.cgi?id=61900

Reviewed by Anders Carlsson.

This is not testable in run-webkit-tests because unless the test is the first to run in an instance
of DumpRenderTree, it is not guaranteed that the full default style sheet has not been initialized.

* css/CSSStyleSelector.cpp:
(WebCore::loadFullDefaultStyle): Replace the simple default print style, which is now equal to the
simple default style, with a new RuleSet before adding the style rules from the full default sheet.
(WebCore::loadSimpleDefaultStyle): Set defaultPrintStyle to point to the default style. They are
equal in the simple case.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@87882 268f45cc-cd09-0410-ab3c-d52691b4dbfc