Remove TestViewType enum from WebUnitTestSupport.h

This was a FIXME for danakj.

BUG=None
TEST=None
R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/387263002

git-svn-id: svn://svn.chromium.org/blink/trunk@178122 bbb929c8-8fbe-4397-9dbb-9b2b20218538