Control font smoothing for layout test in content_shell 

Move the logic for disabling font smoothing for layout tests from
layout_test_helper to content_shell and add a flag for enabling it on a
per test suite basis.

As layout_test_helper is only used for disabling font smoothing on
windows this change also disables the use of that binary on windows and
once the change has rolled the binary itself may be deleted.

R=dpranke@chromium.org,dglazkov@chromium.org
BUG=356780

Review URL: https://codereview.chromium.org/219163008

git-svn-id: svn://svn.chromium.org/blink/trunk@170935 bbb929c8-8fbe-4397-9dbb-9b2b20218538