[Qt] Add getter for JSC TestRunner to DumpRenderTreeQt.
https://bugs.webkit.org/show_bug.cgi?id=113864

Moving setDefersLoading from TestRunnerQt to TestRunner
requires access to the non-Qt TestRunner.
As long as we instantiate both TestRunner and TestRunnerQt,
we need a separate getter for the non-Qt TestRunner instance.

Reviewed by Simon Hausmann.

* DumpRenderTree/qt/DumpRenderTreeQt.cpp:
(WebPage::resetSettings):
* DumpRenderTree/qt/DumpRenderTreeQt.h:
(DumpRenderTree::jscTestRunner):
* DumpRenderTree/qt/TestRunnerQt.cpp:
(TestRunner::setDefersLoading):
    Moving setDefersLoading from TestRunnerQt
    to TestRunner.
* DumpRenderTree/qt/TestRunnerQt.h:
(TestRunnerQt):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147563 268f45cc-cd09-0410-ab3c-d52691b4dbfc