New test cases for the display-grid-set-get.html test.

If an element’s specified display is inline-grid and the
element is floated or absolutely positioned, the computed
value of display is grid.

BUG=79180

Review URL: https://codereview.chromium.org/264373005

git-svn-id: svn://svn.chromium.org/blink/trunk@174600 bbb929c8-8fbe-4397-9dbb-9b2b20218538