Change webkit_unit_tests to use webkit_support.h.

webkit_unit_test_support.h's functions are just thin wrappers that just
call the functions from webkit_support.h. So instead of having this
unnecessary indirection, just call the functions from webkit_support.h
directly.

This is a two side patch. After this lands, Chromium will be update to
remove webkit_unit_test_support.*

BUG=None
TEST=webkit_unit_tests
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/393123005

git-svn-id: svn://svn.chromium.org/blink/trunk@178440 bbb929c8-8fbe-4397-9dbb-9b2b20218538