Per the specification, auto is equivalent to ‘minmax(min-content, max-content)’. Talking with Ojan, this definition is different from the shrink-to-fit behavior (http://www.w3.org/TR/css3-box/#shrink-to-fit): min(max(preferred minimum width, available width), preferred width). It's possible to have the 2 equations applying on the same item (if 'self-align: start' and the grid track is 'auto') so we should check if there is no contradiction here.
We have moved up to a point where we can implement 'auto'. The main minmax bug is kept open so that we can track some issues blocked by the spec (e.g the question of orthogonal flow on grid items).
Created attachment 185517 [details] Proposed implementation: translate auto to minmax in RenderStyle.
Comment on attachment 185517 [details] Proposed implementation: translate auto to minmax in RenderStyle. This seems OK to me, but Ojan suggested putting the handling of auto in RenderGrid.cpp as a helper function. He might have a stronger opinion than I do.
Comment on attachment 185517 [details] Proposed implementation: translate auto to minmax in RenderStyle. Ojan said that it was a slight violation of keeping RenderStyle dumb but he is fine with it due to the limited impact.
Comment on attachment 185517 [details] Proposed implementation: translate auto to minmax in RenderStyle. Clearing flags on attachment: 185517 Committed r141317: <http://trac.webkit.org/changeset/141317>
All reviewed patches have been landed. Closing bug.