This converts Diagnosticable to be a mixin instead of an abstract class, so that it can be used to add diagnostics to classes which already have a base class.

It leaves in place the DiagnosticableMixin mixin, since there are some plugins that are still using it, and removing it would mean that those plugins wouldn't work with master branch Flutter anymore. DiagnosticableMixin will be removed once this mixin version of Diagnosticable makes its way to the stable branch.

* implicit-casts:false in flutter/lib/src/material

* address review comments

* Add a density attribute to ThemeData

* Simplify tests

* Review changes (Hans)

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

This PR adds TargetPlatform.macOS to the TargetPlatform enum. This allows us to begin implementation of some adaptive UI based on which target platform is desired.

I haven't updated the tests here, that will come in a follow-up PR.

* Updated the BottomAppBar to use elevation overlays when a dark theme is used.

* Moved the code for calculating the overlay color to a new utility
ElevationOverlay class and made it private by not including in the material package.

Also updated the documentation for the ThemeData constructor to include
descriptions of parameters that don't map to specific fields directly.

The Material Dark Theme spec has been updated (or soon will be) to clarify that the elevation overlay that is applied to surface colors to indicate elevation should be based off of the colorScheme.onSurface color and not white. This commit implements this change.

* set the copyWith toggleButtonsTheme argument type to ToggleButtonsThemeData

* add a ThemeData.copyWith test

* Added new ButtonBarTheme to replace the deprecated ButtonTheme.bar method.

* Responding to PR feedback.

* [Material] Create material Banner component (#36880)

This PR creates a new material widget for the Banner component. This includes a theme as well. This widget can be dropped into any application, ideally at the top of a listview or scrollview.

(cherry picked from commit 35b6d668)

Removed the use of ButtonTheme.bar in the Banner implementation.

* Updated documentation from PR review comments.

Provide a new ThemeData.from() method that constructs a Theme based off the colors in a given ColorScheme.

This PR creates a new material widget for the Banner component. This includes a theme as well. This widget can be dropped into any application, ideally at the top of a listview or scrollview.

* [Menu] Create Menu theme

* [Menu] Create Menu theme

* [Menu] Formatting changes for Menu theme

* [Menu] Fix spacing difference in theme_data.dart.

* [Menu] Fix spacing difference in theme_data.dart.

* Specifying types

* Formatting changes

* Address PR feedback

* Formatting changes

* Address PR feedback

* Add inherited widget

* Add inherited widget

* Address PR feedback and add inherited widget.

* Formatting changes.

* Address PR feedback

* Address PR feedback

* Address PR feedback

* Address PR feedback

* Introduces ToggleButtons widget

* Introduces ToggleButtonsTheme inherited widget

* Introduces ThemeData.toggleButtonsTheme property

* Implement TooltipThemeData and TooltipTheme

* Add text style property 

* Updated tooltip default colors for light and dark theme to match Material specification

Revert "[Material] Implement TooltipTheme and Tooltip.textStyle, fix Tooltip debugLabel, update Tooltip defaults (#36030)" (#36851)

This reverts commit 62158a1b.

[Material] Implement TooltipTheme and Tooltip.textStyle, fix Tooltip debugLabel, update Tooltip defaults (#36030)

* Implement TooltipThemeData and TooltipTheme

* Add tooltip text style property

* Update default tooltip text style and decoration to match Material specification

* Fix debugLabel incorrectly labeling "white" as "black", and vice versa by default

Added support for a semi-transparent white overlay color for `Material` widgets to indicate their elevation in a dart theme. A new `ThemeData.applyElevationOverlayColor` flag was added to control this behavior, which is off by default for backwards compatibility reasons.

* Add Colors.white38

* Update ThemeData.disabledColor and ButtonThemeData.disabledColor to Colors.white38

* Update pre-existing tests to expect Colors.white38 instead of Colors.white30

* Update API documentation to reflect these changes

This adds support for an animated focusColor and hoverColor to InputDecorator. This color will blend with the background over a fade in period whenever the InputDecorator is focused or hovered, respectively.

It also adds a Listener to the TextField to listen for hover events.

This implements focus and hover handling for Material buttons. It inserts Focus widgets into the tree in order to allow buttons to be focusable via keyboard traversal (a.k.a. TAB traversal), and Listener widgets into the InkWell to allow the detection of hover states for widgets.

Addresses #11344, #1608, and #13264.

* Introduce BottomSheetTheme and shape support for bottom sheet

* Add bottom sheet theme to ThemeData. Use theme in bottom sheet build

* Expose color, elevation, shape to showModalBottomSheet helper

* Expose color, elevation, shape to showBottomSheet helper

* Address PR feedback

* Address PR feedback

* Address additional PR feedback

This PR introduces a number of changes and improvements to snack bars. This includes the ability to specify:

floating style of snack bars that adhere to the updated Material spec
elevation and shape on the SnackBar itself instead of relying on fixed values
a snackBarTheme as part of ThemeData which allows you to customize all of the above on an app-wide level.
This PR is includes the changes from #21484 as well as additional fixes and modifications. Thanks to @NikoYuwono for providing these changes and getting this off the ground!

[Material] Update slider and slider theme with new sizes, shapes, and color mappings (2nd attempt) (#31564)

#30390 was rolled back. This PR will re-roll it forward.

This PR makes a number of changes to the visual appearance of material sliders:

Sizes/Shapes
** enabled thumb radius from 6 to 10
** disabled thumb radius from 4 to 10 with no gap
** default track shape is a rounded rect rather than a rect
**
Colors
** all of the colors now use the new color scheme
** overlay opacity has been reduce from 16% to 12%
** value indicator text color now respects the indicator it is on by using onPrimary
** disabledThumb color no respects the surface it is on by using onSurface
The slider theme is also now constructed consistently with other theme objects within the ThemeData. By default, all values are null, and have default values that are resolved in the slider itself, rather than in the slider theme.

Revert "[Material] Update slider and slider theme with new sizes, shapes, and color mappings (#30390)" (#31339)

This reverts commit b1039f0f.

(This is a temporary revert while some of our customers deal with the breaking changes involved.)

This PR makes a number of changes to the visual appearance of material sliders:

Sizes/Shapes
** enabled thumb radius from 6 to 10
** disabled thumb radius from 4 to 10 with no gap
** default track shape is a rounded rect rather than a rect
**
Colors
** all of the colors now use the new color scheme
** overlay opacity has been reduce from 16% to 12%
** value indicator text color now respects the indicator it is on by using onPrimary
** disabledThumb color no respects the surface it is on by using onSurface
The slider theme is also now constructed consistently with other theme objects within the ThemeData. By default, all values are null, and have default values that are resolved in the slider itself, rather than in the slider theme.