This reverts commit 12a2e682.

Resolved contradictory documentation of showGeneralDialog and default value of 'barrierLabel' argument (#78890)

* Create state restoration templates, 

* Update existing state restoration samples to use the new templates

* Add to README, decided to require stateful widgets to include RestorationMixin

Update samples to use repo analysis options, Fix sample templates and a ton of analyzer issues (#77868)

* Minor doc, style, and perf updates to Navigator/Routes

These are minor fixes I ended up making while working on a larger
project that never went anywhere.

- Used a ColoredBox instead of a DecoratedBox for ModalBarrier
  (probably a trivial memory/perf win).

- A bunch of Navigator documentation fixes around when things rebuild.

- Mark routes dirty when the Navigator has a dependency change. I
  cannot find a way to test this because as far as I can tell it makes
  no actual difference to when things rebuild because whenever the
  Navigator rebuilds the Overlay rebuilds and whenever that happens
  every OverlayEntry rebuilds, but in theory that's not guaranteed so
  this is sort of a correctness fix. It may even be a perf loss. We do
  something similar in didUpdateWidget already. I could be convinced
  to maybe remove these...

- Make ModalRoute.filter public like everything else.

- Made ModalRoute update its barrier when it gets an update, in case
  e.g. the modal barrier depends on inherited widgets via the
  navigator context. Again, not sure of any way to detect this, it
  might actually be moot, but it seems to be the technically correct
  solution?

- Minor style fixes.

All in all I couldn't figure out a way to test any of this (I wrote
multiple large tests but it turns out they all already pass on master
and are effectively redundant with existing tests).

* Remove extraneous blank line

Adds Navigator.maybeOf to replace calling Navigator.of(context, nullOk: true), and removes the nullOk parameter. Also changes Navigator.of to return a non-nullable value, and removes many (120!) instances of the ! operator, reducing the possible places where a null dereference could occur.

This reverts commit 9b56241e.

This reverts commit 1f0df545.

* Reland "Nnbd widgets (#64672)"

This reverts commit 127e6790.

* remove non-nullable enforcement on AsyncSnapshot

* make data param non-nullable for AsyncSnapshot.withData

* make some Text params non-nullable

This reverts commit e682ec71.

* migrate widget to nullsafety

* remove double blank line after license

* address review comments in actions.dart

* nullable ObjectKey.value

* use local variable oldElement

* make State.build non-nullable

* make State.context non-nullable

* newline at eof

* make ProxyWidget.child non-nullable

* make _InactiveElements.debugContains non-nullable

* make Element.depth non-nullable

* make ProxyElement.build non-nullable

* make StatefulElement.state non-nullable

* remove 'Notice that'

* avoid cast of list in RenderObjectElement.updateChildren

* make IndexedSlot.value non-nullable

* avoid cast of list in MultiChildRenderObjectElement.mount

* make some WidgetsApp parameters non-nullable

* hitTest take non-nullable position

* make ScrollableState.position non-nullable

* use _pixels instead of pixels

* make ViewportOffset.pixels non-nullable

* make param and return type of IndexedWidgetBuilder non-nullable

* unused_import

* make context param non-nullable for Builder in animated_list.dart

* make ScrollMetrics.viewportDimension non-nullable

* make ScrollMetrics.{min,max}ScrollExtent non-nullable

* make _Location.file non-nullable

* _WidgetForTypeTests.createElement throw UnimplementedError

* update _NullWidget.build error message

* make _ShortcutsState.manager non-nullable

* Fix childCount issues for NNBD

* fix childCount computation on web

* increase max value on js side to compute childCount

* make aspect parameter of dependOnInheritedWidgetOfExactType nullable

* merge has{min,max}ScrollExtent into hasScrollExtents

* update focus_manager.dart

* address review comments in icon.dart

* address review comments in image.dart

* address review comments in routes.dart

* address review comments in scroll_activity.dart

* update doc comments

* make UserScrollNotification.direction non-nullable and required

* rename hasScrollExtents to hasContentDimensions

* unnecessary late
Co-authored-by: Ian Hickson <ian@hixie.ch>

Updated references to the old button classes to the new ones in comments and documentation for classes in the widgets, services and rendering libraries. (#62099)

https://github.com/flutter/flutter/issues/31931

`showDialog()` and `showGeneralDialog()` were allowing transparent
colors but then triggering an assertion down the stack while building
the modal barrier. The assertion existed to keep from animating from
transparent to transparent, but there's no need for the assertion,
since we can just treat the transparent case as the same as the null
case -- no animation necessary.

The function passes most of its arguments through to
`_DialogRoute`, but it wasn't providing the default
values that `_DialogRoute` was, causing it to override
the defaults will null values.