Somehow I missed these in my previous patch.

Fixes #3503

* Make IconButtons as big as possible

This makes it easier to use e.g. AssetImage in simple test applications.

Also, dartdoc improvements.

Also, use @required in one place, to see if it causes any trouble. If it
doesn't, I'll start using it in more places.

+ 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.

Also fill in some related dartdocs.

Previously, we lost sync with the tab view contents when switching tabs. Now we
key the subtrees to make sure they keep their state across tab animations.

Fixes #3147

This patch adds dartdoc to LazyBlock. Also, this patch fixes the scrolling
physics of LazyBlock. Previously, we updated a running simulation only when the
change in scroll behavior changed the current scroll offset. Now we update
running simulations every time the behavior changes because the simulation
might depend on quantities other than the current scroll offset.

LazyBlock is intended as a replacement for MixedViewport. Rather than

maintaining a table of all the observed child sizes (like

MixedViewport), LazyBlock works by dead reckoning the location of the

children based on the existing viewport. This approach makes it easier

to resize children because LazyBlock doesn't cache any additional

information that would need to be invalidated.



This patch contains a first draft of LazyBlock that works in a simple

usage scenario. Subsequent patches will replace

ScrollableMixedWidgetList with LazyBlock and port the existing

ScrollableMixedWidgetList tests over to LazyBlock.



Related to #3075

If we use null for these values, the implementations will later assert.



Fixes #3102

For example, to implement backdrop blur effects.

This way, widgets that try to use the DefaultTextStyle don't have to

handle the case where there isn't an explicit default.

- Add x and y to the parent data, in case it's useful. In point of fact,
  I ended up not needing it.

- Make columnWidths settable rather than having a setter so that the
  code in the widgets layer is more idiomatic.

- Teach setFlatChildren about avoiding unnecessary drop/adopt loops.

- Assert that the child list length is correct more aggressively so that
  we catch the dumb bug I had more quickly next time.

- Improve the toString() to handle empty tables better.

- Resort the imports in framework.dart.

- Introduce a LocalKey for cases where you don't want to allow use of
  GlobalKey.

- Make inflateWidget and deactivateChild public for subclass use.

- Table widget.

- Cell widget.

- TableRow fake widget.

This provides an easy way to do implicit opacity transitions.

Fixes #2873

...followed all the way back to ImageCache, ImageInfo, ImageProvider,
and friends.

New RenderAligningShiftedBox abstract class for render boxes with
"alignment", which as of now is:

 - RenderPositionedBox
 - RenderConstrainedOverflowBox (ex RenderOverflowBox)
 - RenderSizedOverflowBox
 - RenderFractionallySizedOverflowBox (ex RenderFractionallySizedBox)

(The respective widgets are Align, OverflowBox, SizedOverflowBox, and
FractionallySizedBox. They haven't been renamed.)

Also I added some toString details.

This patch adds a consistent, simple description for the common pattern of
having a single child widget.

The old text was misleading because it was written when RichText was an
implementation detail of Text.

Fixes #2624

* justifyContent -> mainAxisAlignment
* alignItems -> crossAxisAlignment
* FlexJustifyContent -> MainAxisAlignment
* FlexAlignItems -> CrossAxisAlignment

Fixes #231

This patch renames StatelessComponent to StatelessWidget and
StatefulComponent to StatefulWidget.

Fixes #2308

Fixes #1482

Fixes #1382

Fixes #774

Fixes #581

And fix the zillion issues that uncovered.

This reverts commit f41b3411, reversing
changes made to e33d8d96.

This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.

This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640

And fix the zillion issues that uncovered.

If there's not enough height for the given aspect ratio, we now try to see if
using the height to infer the width will fit the given constraints. The
algorithm we use is similar to the one we use for RenderImage.

Fixes #2620

Transform applies its transform before painting, but sometimes you want
the widget to layout after its transform has been applied. We can't
handle general tranforms in this way because we can't couple width and
height constriants, but we can handle certain rotations.

Fixes #1214

We'll need this for RTL support because the RTL state will live in the widget
tree. Also, remove the `oldWidget` argument to updateRenderObject because there
aren't any clients for it.

This patch prepares us to pass a BuildContext to RenderObjectWidgets, which
will make it possible to rebuild RenderObjectElements:

 * Delay creation of the render object until mount(). That will let us pass
   `this` to createRenderObject and have the inherited elements be initialized.

 * Cleanup widgets that take builder closures to prepare for their
   RenderObjectElement to be rebuilt more often.

 * Add a test for the interaction between inherited widgets and
   MixedViewport.

Related to #2598