DevTools: Fix spinner icon blue background

The spinner icons background should match the sidebar color, so
the patch removes spinners with blue background and makes it
always use spinners with grey background.

R=loislo@chromium.org, pfeldman@chromium.org

Review URL: https://codereview.chromium.org/169093006

git-svn-id: svn://svn.chromium.org/blink/trunk@167350 bbb929c8-8fbe-4397-9dbb-9b2b20218538