DevTools: Replace Apple styled spinner icon with Chromium one.

Drive-by: replace animated PNG files with a CSS animation.

R=yurys@chromium.org

Review URL: https://codereview.chromium.org/181433002

git-svn-id: svn://svn.chromium.org/blink/trunk@167914 bbb929c8-8fbe-4397-9dbb-9b2b20218538