+ Add new demo to gallery to show data tables. (This currently doesn't
use a Card; I'll create a Card version in a subsequent patch.)
+ Fix checkbox alignment. It now centers in its box regardless.
+ Add Colors.black54.
+ Some minor fixes to dartdocs.
+ DataTable, DataColumn, DataRow, DataCell
+ RowInkWell
+ Augment dartdocs of materia/debug.dart.
+ DropDownButtonHideUnderline to hide the underline in a drop-down when
used in a DataTable.
+ Add new capabilities to InkResponse to support RowInkWell.
+ Augment dartdocs of materia/material.dart.
+ Add an assert to catch nested Blocks.
+ Fix a crash in RenderBox when you remove an object and an ancestor
used its baseline. (https://github.com/flutter/flutter/issues/2874)
+ Fix (and redocument) RenderBaseline/Baseline.
+ Add flex support to IntrinsicColumnWidth.
+ Document more stuff on the RenderTable side.
+ Fix a bug with parentData handling on RenderTable children.
+ Completely rewrite the column width computations. The old logic made
no sense at all.
+ Add dartdocs to widgets/debug.dart.
+ Add a toString for TableRow.
