It was failing in the case of an AppContext being in scope
but not having a `BotDetector` seeded in it.

* Fix SliverPadding dropping the chain on scrollOffsetCorrection propagation

* review doc

* Fix focus switching when changing tabs in CupertinoTabScaffold

* review

* Test focuses are saved within tabs

* review

* add a FAB NotchMaker to ScaffoldGeometry

* add a notchMaker to FloatingActionButton

* Initial implementation of BottomAppBar

Mainly includes the notch making logic.
Not yet tested as currently there is no way to make the FAB and the BAB
overlap, once #14368 to lands we could add unit tests to the
BottomAppBar as well.

* use a closeable for clearing the FAB notchmaker

* Fix packages tests when run off bots

* Tweak dependencies to make bots happy

* Review comment

https://github.com/flutter/flutter/issues/14519

https://github.com/flutter/flutter/issues/14798

Fixes https://github.com/flutter/flutter/issues/14751

* Fix snapshot fingerprint check for --preview-dart-2.

* Remove printTraces

These URLs all automatically redirect HTTP to HTTPS so makes sense to point users at the secure versions.

This will allow other tools to call into the roll_dev script
to know what version is about to be published without actually
publishing.

https://github.com/flutter/flutter/issues/14751

* fix potential call on null

* review

This is needed to support running with local engine's dart sdk.

This is follow-up to https://github.com/flutter/flutter/pull/14702.

* All lists produced by JSON parsing are List<dynamic>. If more
speficic type is required then they need to be explicitly cast, e.g.
using castFrom helper;
* Function of type (ByText) -> Finder is not a subtype of
(SerializableFinder) -> Finder because ByText is in the contravariant
position;
* In Dart 2 typed(any) should be used instead of any in mockito based
tests.

* Added sample code to AnimatedOpacity docs

Merging on red tree to get back to green.