Before this change, if you specified a non-null textTheme, but the theme you specified didn't have a body2 defined, then creating a ChipTheme would assert (which means creating a ThemeData would fail).

This adds handling for this corner case to default to reasonable values in that case. The slider had the same problem, but for accentTextTheme, so I fixed that too.

While I had the patient open, Hans and I noticed that TextTheme.merge wasn't doing the right thing in the case where some members were null either, so I fixed that, and added some examples, since merge/copyWith are common operations that are not always well understood.

Fixes #17251

This chip demo is more interactive than the last one, trying to exercise all of the types of chips for a demo that lets you select different types of "chips" (like tortilla, wood, micro, etc.), and then filter them and select an action on them.

This converts the chips to use a ChipThemeData to get most of their customization values from (if not overridden by specific arguments to the chip constructors), and to have the base ThemeData contain one of these. It also adds the ChipTheme widget that will allow overriding the theme for a particular subtree in the widget hierarchy.

Added tests for both, and just more tests in general for the Chips.

This adds a slider demo with a custom theme to the gallery.

In the process of adding this, I decided to add a text theme to the SliderThemeData, since it's a pain to change the text style on the value indicator otherwise.

* change ThemeData.primaryColor to PrimarySwatch instead of PrimarySwatch[500]

* fix mismatched color in stock test case

This allows other code to get the same style without having to know exactly it is computed.

Fixed the real repaint problem the Slider had (missing addListener), and added tests for it.

Added GlobalKey reparenting test.

Added the ability for the value indicator to slide left and right to avoid falling off the edge of the screen.
It only shifts as much as it can without deforming, but even at large text scales, that is enough to keep the text on the screen.

Updated the formatting on theme_data.dart and others to use longer line length.

Also, removed a color tween that faded the value indicator in as it scaled, since that wasn't to spec.

* spelling: accommodate

* spelling: allotted

* spelling: anonymous

* spelling: artificial

* spelling: associated

* spelling: asset

* spelling: button

* spelling: canvas

* spelling: compatibility

* spelling: coverage

* spelling: condition

* spelling: decoration

* spelling: deferring

* spelling: diameter

* spelling: direction

* spelling: displacement

* spelling: dropdown

* spelling: needing

* spelling: environment

* spelling: exited

* spelling: expansion

* spelling: explore

* spelling: families

* spelling: horizontal

* spelling: increment

* spelling: indices

* spelling: internationalization

* spelling: labrador

* spelling: localizations

* spelling: midflight

* spelling: milliseconds

* spelling: minimum

* spelling: multiple

* spelling: multiplication

* spelling: navigator

* spelling: overridden

* spelling: package

* spelling: performance

* spelling: platform

* spelling: porsche

* spelling: position

* spelling: preceded

* spelling: precede

* spelling: precedence

* spelling: print

* spelling: property

* spelling: readily

* spelling: reproducibility

* spelling: rounded

* spelling: scroll

* spelling: separate

* spelling: separator

* spelling: services

* spelling: specific

* spelling: specify

* spelling: synchronously

* spelling: through

* spelling: timeout

* spelling: triangle

* spelling: trivial

* spelling: unusual

* spelling: then

* spelling: vertically

* spelling: visible

* spelling: visited

* spelling: voice

This implements an update to the look of the Slider widget.

Specifically, it does the following:

* Adds the ability to customize the colors of all components of the slider
* Adds the ability to customize the shape of the slider thumb and value indicator
* Adds the ability to show the value indicator on continuous sliders
* Updates the default value indicator to be a "paddle" shape with new animations.
* Changes the tick marks to be visible all the time on discrete sliders
* Fixes a memory leak of an animation controller.
* Removes "thumbOpenAtMin" flag, which is no longer needed, and can be emulated by the
custom thumb shape support. It was not widely used.
* Adds tests for all of the new features.

* Small glow overscroll dartdoc addition

* Directly specify [MaterialApp]

* review

This cleans up lerp, lerpFrom, lerpTo, and scale methods, and their
documentation.

Fixes https://github.com/flutter/flutter/issues/12377.

* remove extracted methods

* lint

* Theme provides all TextStyle properties

* match field declaration order in the test

* Theme.of returns text style with inherit == false

* change TextStyle.inherit logic; docs

* add TextStyle.debugLabel

* address comments

* add debug labels to Typography text styles

* optimize ThemeData: make it monomorphic, memoize result

* address comments

* RLU cache; fix text theme merging

* use FIFO cache for ThemeData; use HashMap to store inherited widgets

* address comments

* introduce localized text geometry in MaterialLocalizations

* remove geometry from color text themes

* fix merge conflict

* optional Localizations

* fix fallback; test; docs

Moved everything icons related except the material icon button and the materialicon font list to widget

If the caller doesn't explicitly give the brightness of the primary
color, we now estimate it using an algorithm from the Web Content
Accessibility Guidelines.

Also, this patch contains a function that converts RGB colors to
HSVColors. I was originally going to use that, but the WCAG algorithm
ended up seeming like a better choice. The patch still includes this
function because it's generally useful.

Fixes #5718

* more widget const constructors

* prefer const constructors

* address review comments

Turns out we have many immutable classes.

Fixes #6892

* add @required when there's an assert not null

* address review comments

Otherwise it's somewhat verbose to configure all the text themes.

Covers lib/ in package:flutter.