[LayoutNG] Make NGBlockLayoutAlgorithm accept a NGBlockNode.

Instead of the LayoutObject, Style, FirstChild tuple.

This is so that NGFragmentBuilder can access the node to construct a
break token correctly.

See prototype multi-col patch: crrev/2693193002.

BUG=635619

Review-Url: https://codereview.chromium.org/2692403003
Cr-Commit-Position: refs/heads/master@{#450843}
10 files changed