DevTools: add test to verify simple selector behavior.

DOMPresentationUtils.simpleSelector behavior used to be fixated in a
couple of tests that dumped default selector in a new style rule section.
This patch adds a separate test for simpleSelector method and removes
the calls to default selector in the affected tests.

This makes it possible to use InspectorTets.addNewRule in these tests

Review URL: https://codereview.chromium.org/458213002

git-svn-id: svn://svn.chromium.org/blink/trunk@179952 bbb929c8-8fbe-4397-9dbb-9b2b20218538