DevTools: [SSP] fix memory leak through settings

The patch fixes two memory leaks happenning through showInheritedStyle
setting.

BUG=397228
R=vsevik

Review URL: https://codereview.chromium.org/648823004

git-svn-id: svn://svn.chromium.org/blink/trunk@184054 bbb929c8-8fbe-4397-9dbb-9b2b20218538