This fixes the issue that currently we use "auto" as initial value for
grid-template-column and grid-template-rows although spec says it
should be "none". This makes a lot of difference for these properties
because currently we represent "auto" as a list with one auto-sized
track which means initial value for grid-template-column defines one
"explicit" track while it should define none of them.
This change makes grid-auto-columns/rows be applied to the correct
tracks when initial values is used for grid-template-column/rows.
