Sync Android <video controls> with the default controls

Add back the rounded border and the bottom 5px padding.

BUGS=251244

Review URL: https://chromiumcodereview.appspot.com/17382003

git-svn-id: svn://svn.chromium.org/blink/trunk@158344 bbb929c8-8fbe-4397-9dbb-9b2b20218538