The problem was that grid shorthand has the following longhands:
grid-template, grid-auto-flow, grid-auto-columns and grid-auto-rows.
And grid-template is a shorthand again, which was not being expanded
properly when inherit was parsed.

This is fixed if we only use longhands to define the property in
CSSProperties.in.

Added the inherit case in the grid shorthand test.

BUG=408989
TEST=fast/css-grid-layout/grid-shorthand-get-set.html

Review URL: https://codereview.chromium.org/564133004

git-svn-id: svn://svn.chromium.org/blink/trunk@182045 bbb929c8-8fbe-4397-9dbb-9b2b20218538