DevTools: Fix CSS syntax errors in layersPanel.css and sourcesView.css

TBR=vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/133823002

git-svn-id: svn://svn.chromium.org/blink/trunk@164871 bbb929c8-8fbe-4397-9dbb-9b2b20218538