Fixes #5215

Fixes #11381

Fixes #11373

Fixes #11374

When scrolling vertically, the scrollbar is on the left in RTL.

Fixes #11369

Fixes #11358

* Notify the completer after the close animation completes on the snackbar

* Review comments

* Fix tests and analyzer warnings

* Fix analyzer warnings

* Introduce a Directionality inherited widget which sets the ambient LTR vs RTL mode (defaulting to null, which means you cannot use directionality-influenced values).

* Make it possible to configure Padding (including Container.padding and Container.margin) using a directionality-agnostic EdgeInsets variant.

* Provide textDirection and verticalDirection controls on Row and Column to make them RTL-aware.

* Introduce a variant of FractionalOffset based on the EdgeInsets variant. Not yet actually used.

* Fix all the tests that depended on Row defaulting to LTR.

* refactor to ensureAction + some related doc fixes

* Update docs for markNeedsSemanticsUpdate

* rewording

* rewording

* ensureAction test

* ensureAction test

* ensureAction test

* more tests

* refactor to allways reset node

* tiny fixes

* more test

* doc fixes

* one more test

* review comments

* Properly update semantics when Material/Cupertino Slider are disabled

* whitespace fix

* fix style

Bare bones widget inspector support.

Toggle the widget inspector from the flutter tool by pressing 'i'.
When the widget inspector is select mode:
Pointer down to to inspect a widget.
Pointer click to finalize selection of a widget. You can now interact
with the application as you normally would but with the inspected widget
highlighted.
Click the inspect icon in bottom left corner of screen to reactivate
select mode.

when describing non-nullable method arguments.

Some widgets are using closures even if the only values that are
captured are this, context or widget, that can be accessed even from
methods of the State object.

* Let the initial date picker mode be selectable

* Doc for enum

* Add a test

* Add a comment for test

* actually decouple test from setup state

* Wrap the label widget of the Chip in a Flexible. (#11523)

* This allows the Chip to constrain the size of its content after taking into account the space occupied by the avatar and delete icon (if they are present)

* Adding unit tests to evaluate correct size constraints of the Chip widget's label. (#11523)

* Minor change in formatting.

* Adjust function formatting.

* a11y: handle left/right scrolls correctly

* fix keep alive test

* fix scaffold test

* Allow tapping on TabBar indicator to switch tabs

* fix semantics

* review comments

* Adds more customization options to the Chip widget

Includes:
- Custom Tooltip message for the delete button;
- Custom background color for the chip
- Custom delete icon color
- Custom label text style

* Adds missing type annotations to tests and improves documentation.

* Tweaks labelStyle field documentation

Add Diagnosticable base class and documentation

* PopupMenuButton: create IconButton if child is Icon

Otherwise the resulting button has an abnormally small and rectangular
area. With multiple PopupMenuButton(child: Icon) they get squished
together in the AppBar.

* Add separate icon argument to PopupMenuButton

* Fix style issues and tweak dartdocs

* Add tests for icon argument to PopupMenuButton

* Group icon tests and fix broken test, analyzer warnings

* Test that the correct custom icon is present

* Apply De Morgan's to work around dart analyzer bug

see: https://github.com/dart-lang/sdk/issues/30288

It has recently come to light that we may have been ordering saveLayer
calls and clip calls incorrectly.

Refactor RenderObject.toStringDeep and Widget.toStringDeep code to use DiagnosticsNode.

* Support automaticallyImplyLeading param in AppBar

* Review fixes

* fix review comments

Mainly, this adds documentation to members that were previously
lacking documentation.

It also adds a big block of documentation about improving performance
of widgets.

This also removes some references to package:collection and adds
global setEquals and listEquals methods in foundation that we can use.
(setEquals in particular should be much faster than the
package:collection equivalent, though both should be faster as they
avoid allocating new objects.) All remaining references now qualify
the import so we know what our remaining dependencies are.

Also lots of code reordering in Flutter driver to make the code
consistent and apply the style guide more thoroughly.

* Prefix and Suffix support for TextFields

* Adding Tests

* Removing spurious newline.

* Fixing a small problem with the test

* Code review changes

* Code Review Changes

* Review Changes

* Export the new StrokeJoin enum

* Added example for line styles, and enabled line join styles.

* Reverting inadvertent change to main.dart.

* Updated due to code review of engine code

* Removed example.

* Added arguments to named routes, with test.

* Fixing some formatting

* Fixing Navigator.pop for named routes.

* Fixing comment.

* Simplifying test.

* Fixing new -> const for Text object.

* Tiny text change (also to kick a new Travis build)

* Added a more realistic test case.

* Reverting unintentional iml changes.

* Fixing trailing newline

* Removing some changes that snuck in.

Extract common text selection overlay logic from Material to Widget and create a Cupertino version of the overlays

* adds inactiveColor and showThumb to Slider

* add customizable color and showThumb tests

* remove showThumb, add negative tests

See https://github.com/flutter/flutter/issues/11168

Fixes https://github.com/flutter/flutter/issues/10917