lint-test-expectations should check that the SmokeTests list is kept up to date.

If developers move or delete LayoutTests, and those tests are listed in SmokeTests,
we should complain when linting the test expectations, just like we would if
the tests were listed in TestExpectations.

R=ojan@chromium.org, peter@chromium.org
BUG=321863

Review URL: https://codereview.chromium.org/77623003

git-svn-id: svn://svn.chromium.org/blink/trunk@163823 bbb929c8-8fbe-4397-9dbb-9b2b20218538