Add tests to avoid regeression on textarea.

LayoutTests/fast/forms/input-tab-shows-caret.html:
 Confirms tab fusing shows up caret. Needs rebaseline.

LayoutTests/fast/forms/textarea-select.html:
 textarea.select() selects right range of a value text.

BUG=399999, 400320, 400180

Review URL: https://codereview.chromium.org/444493003

git-svn-id: svn://svn.chromium.org/blink/trunk@179518 bbb929c8-8fbe-4397-9dbb-9b2b20218538