QtTestBrowser should provide way to clear selected elements
https://bugs.webkit.org/show_bug.cgi?id=107437

Reviewed by Simon Hausmann.

Provide a way to "Clear selection" in the "Develop" menu to clear the previous search highlight.
Invoke the clearSelection prior to highlighting new elements.

* QtTestBrowser/launcherwindow.cpp:
(ElementHighlight):
(LauncherWindow::createChrome):
(LauncherWindow::selectElements):
(LauncherWindow::clearSelection):
* QtTestBrowser/launcherwindow.h:
(LauncherWindow):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140323 268f45cc-cd09-0410-ab3c-d52691b4dbfc