* Revert "Construct the accessibility channel's events by SemanticsEvent. (#12638)"

This reverts commit 4c1150dd.

* Revert "Revert "Add a way to get the furthest Navigator" (#12608)"

This reverts commit 79f13c36.

* Revert "BoxDecoration.borderRadius and RoundedRectangleBorder.borderRadius RTL (#12603)"

This reverts commit 07908916.

* Revert "Copy snapshot file into assets (#12523)"

This reverts commit f6135107.

* Revert "Add a rootNavigator option to Navigator.of (#12580)"

This reverts commit 822084b2.

Most of the framework widgets should work in terms of EdgeInsetsGeometry
rather than EdgeInsets so that their clients can supply directional
insets.

Fixes https://github.com/flutter/flutter/issues/9342

* make @immutable const

* fix build

Nobody knew what a Block was.

The latter is the proper spelling.

Fixes #8883

In some situations, dialogs don't want the barrier to be dismissable.

Fixes #8354

The demo of the SimpleDialog had some useful code that should really be part of
the framework. This patch extracts it into a SimpleDialogOption widget.

Remove debugCheckHasScaffold because it is unused.

Also, add tests for InkWell, SimpleDialog, and other widgets.

This patch adds tests for radio buttons, the date picker, as well as a
number of other classes.

Change `Flexible`'s default `FlexFit`

Previously, `Flexible` defaulted to `FlexFit.tight`, which forced the child to
expand to fill the available space. Now, `Flexible` defaults to
`FlexFit.loose`, which does not force the child to expand to fill the available
space.

If you want the child to expand to fill the available space, consider using
`Expanded` instead.

Fixes #5169

Fixes #7375

This fixes minor issues I ran into while using Flutter.

These futures complete when the route is popped off the navigator. This
generalizes and simplifies a mechanism already in place for dialogs and
menus.

Fixes #5283

Fixes #988

We were trying to cram too much functionality in to the Dialog widget. Now we
have AlertDialog and SimpleDialog to cover to two different kinds of dialogs in
the spec.

Rather than scrolling the entire contents of the dialog, we should instead
scroll only the part between the title and the button bar.

Also, polish up the padding in the simple dialog demo.

Fixes #6057

This API is the front-end part of the work on showing licenses.

Future patches will:

* Provide an API for registering what licenses should be shown here,
  which will be used by this feature to shown licenses but could also be
  used by custom code for showing licenses (e.g. for people not using
  the Material widgets).

* Actually populate this license API from all the licenses we currently
  use in the engine, in the framework, and from any pub packages that
  are used (directly or indirectly) by the application.

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

Also renames ButtonTheme.footer to ButtonTheme.bar.

Fixes 3544

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

This reverts commit 55f9145e.

Turns out that this commit breaks apps that use the material library,
because of the _errorTextStyle DefaultTextStyle which has inherit:true.
Just setting it to false doesn't work, unfortunately, because then you
hit some sort of issue with merging that text style with others that
have inherit:true.

To make it clear that this constructor requires an explicit style. Also
throw a descriptive error recommending the inherit constructor for
styles with the inherit bit set.

Fixes #3842

Instead of incorporating the margin into the button, introduce a ButtonBar
widget that supplies the proper spacing between the buttons. Also, make these
buttons more configurable via ButtonTheme so that dialogs can change the
minWidth and padding of the buttons as required by the spec.

Fixes #1843
Fixes #3184