Encoding API: Layout test tidying

Make quotes consistent, use filter(), show more detail in test names.

TBR=jshin@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/269663004

git-svn-id: svn://svn.chromium.org/blink/trunk@173099 bbb929c8-8fbe-4397-9dbb-9b2b20218538