Update transformed-text-fill-pattern.html.

r154124 (https://codereview.chromium.org/18178017) opportunistically removed the clipPath, but it
turns out it's still needed on some platforms.

Switching to plan B: revert the clipPath change and add an empty <text> element to force mask-based
clipping (which the reftest unfortunatelly depends on).

TBR=vsevik@chromium.org

Review URL: https://codereview.chromium.org/18833004

git-svn-id: svn://svn.chromium.org/blink/trunk@154130 bbb929c8-8fbe-4397-9dbb-9b2b20218538