DevTools: [network] make timing colors consistent in popover and tab, remove box shadows and round borders.

R=eustas@chromium.org, vsevik@chromium.org

Review URL: https://codereview.chromium.org/474453002

git-svn-id: svn://svn.chromium.org/blink/trunk@180198 bbb929c8-8fbe-4397-9dbb-9b2b20218538