Unify filter-bar UI.

1) Make text-filter padding consistent across all panels.
2) Remove line between filters and network panel

BUG=347043

Review URL: https://codereview.chromium.org/248993003

git-svn-id: svn://svn.chromium.org/blink/trunk@172472 bbb929c8-8fbe-4397-9dbb-9b2b20218538