Fix the baseline calculation for <textarea>

We want the baseline of a textarea to be the bottom of the margin box in all
cases. Therefore, we also need to override inlineBlockBaseline. This only
matters in a somewhat unusual DOM where a display: block <textarea> gets
put into an inline-block.

I broke this in r159173 / https://codereview.chromium.org/26454004

R=ojan@chromium.org,leviw@chromium.org
BUG=321486,304210

Review URL: https://codereview.chromium.org/86483005

git-svn-id: svn://svn.chromium.org/blink/trunk@162704 bbb929c8-8fbe-4397-9dbb-9b2b20218538