Now IconThemeData.fallback is a factory constructor and IconThemeData.of() does
the work of computing the fallback for its clients.

Also, add tests for ImageIcon and ListItems.

Based on observations of usability study participant P1.

This feature is the implementation of an accessibility feature that changes the
size of text by a constant factor.

Fixes #5873

Anywhere that accepted IconData now accepts either an Icon or an
ImageIcon.

Places that used to take an IconData in an `icon` argument, notably
IconButton and DrawerItem, now take a Widget in that slot. You can wrap
the value that used to be passed in in an Icon constructor to get the
same result.

Icon itself now takes the icon as a positional argument, for brevity.

ThemeData now has an iconTheme as well as a primaryIconTheme, the same
way it has had a textTheme and primaryTextTheme for a while.

IconTheme.of() always returns a value now (though that value itself may
have nulls in it). It defaults to the ThemeData.iconTheme.

IconThemeData.fallback() is a new method that returns an icon theme data
structure with all fields filled in.

IconTheme.merge() is a new constructor that takes a context and creates
a widget that mixes in the new values with the inherited values.

Most places that introduced an IconTheme widget now use IconTheme.merge.

IconThemeData.merge and IconThemeData.copyWith act in a way analogous to
the similarly-named members of TextStyle.

ImageIcon is introduced. It acts like Icon but takes an ImageProvider
instead of an IconData.

Also: Fix the analyzer to actually check the stocks app.

As of `1.18.0-dev-0`, these cases will get flagged.  In the meantime, the

Fixes 3544

This patch starts working through the missing dartdocs in widgets.dart.

* Remove IconThemeData.clampedOpacity

+ 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.

* styles updates for the api docs

* update library docs

* use the new --favion and --use-categories options for dartdoc

Now past halfway though material.dart by files.

This patch renames StatelessComponent to StatelessWidget and
StatefulComponent to StatefulWidget.

Fixes #2308

Fixes #2361

This enum doesn't make sense anymore now that we can arbitrarily colorize
icons.  Instead, we just use a Color, which is both simpler and can be
interpolated during animations.

Fixes #1279

Rather than managing all the Material Design icons manually, we now
manage them using an icon font. The icon font contains glyphs for each
icon in an efficient vector format.

This patch updates the FLX tooling to include the MaterialIcons font and
updates the Icon widget to use the font instead of asset images.

Fixes #2313
Fixes #2218
Fixes #2009
Fixes #994

This makes it match the material spec more.
https://www.google.com/design/spec/style/icons.html

Fixes https://github.com/flutter/flutter/issues/1357

Add support for the appbar behavior described in the "Flexible space with image" section of https://www.google.com/design/spec/patterns/scrolling-techniques.html#scrolling-techniques-scrolling.

Now you can colorize an Icon simply by proving a Color for the Icon.

The name of the parameter wasn't consistent with IconButton or DrawerItem, etc.

Fixes #1871

Material design icons are defined to work at specific sizes: 18, 24, 36, 48.
The current API doesn't reflect that and just takes a size int. If an invalid
size is chosen an error is printed to the console and no icon shows up.

Fixes #1816

Now AssetImage will look in the default bundle if you don't supply an explicit
bundle.

Fixes #680

Provide a way to schedule a callback for immediately after the current
frame has been sent to the GPU thread. This is useful for times where
you want to immediately schedule yourself for another build or layout
because, for instance, you just displayed frame zero of an animation and
you want to use the metrics from that layout to set up the actual
animation to begin immediately, such that the very next frame is frame 1.

Instead of requiring clients to use ui.ColorFilter, we show show the
ColorFilter class, similar to what we do for Color.

A MaterialList understands the sizing, padding, and scrollbar features of
Material Design lists.

Also, add CircleAvatar for showing the circular avatars that are commonly used
in material lists.

- truncate pixel values to 1dp since there's really no point being told
  the Size is 302.98732587287 by 648.28498579187.

- describe more Widgets so that debugDumpApp() is more useful.

- remove bufferValue from ProgressIndicator (cc @hansmuller) since it's
  not yet implemented.

- half-hearted toString() for ThemeData. There's no point making a
  complete one, since it would cause line-wrap even on big monitors in
  debugDumpApp dumps, and you can easily get the actual values from a
  debugging if that's the issue.

- flesh out BoxConstraints.toString() so that fully unconstrained and
  fully infinite constraints are called out explicitly. I experimented
  with adding even more special cases, e.g. calling out unconstrained
  widths with fixed heights, etc, but it made the output less readable.

- remove a redundant _updateVariable() in AnimatedContainer (cc
  @abarth).

- add more information to RenderView.toString().

Add type annotations in many places.
Fix some identifiers to have more lint-satisfying names.
Make all operator==s consistent in style.
Reorder some functions for consistency.
Make ParentData no longer dynamic, and fix all the code around that.

These are now part of material.dart.