It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

They should fail, because we don't have real support yet.

Also, make the debug override work in release builds, so that people
on those platforms have a workaround.

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 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.

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

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

I got tired of drive-by spelling fixes, so I figured I'd just take care of them all at once.

This only corrects errors in the dartdocs, not regular comments, and I skipped any sample code in the dartdocs. It doesn't touch any identifiers in the dartdocs either. No code changes, just comments.

* 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

Turns out we have many immutable classes.

Fixes #6892

Teach `paints` matches about `drawRect` and how to `paintChild`.

Also, improve test coverage.

Fixes #7375

On Android and Fuchsia, default to Roboto. On iOS, use San Francisco.

Fixes #5916

This API is the front-end part of the work on showing licenses.

Future patches will:

* Provide an API for registering what licenses should be shown here,
  which will be used by this feature to shown licenses but could also be
  used by custom code for showing licenses (e.g. for people not using
  the Material widgets).

* Actually populate this license API from all the licenses we currently
  use in the engine, in the framework, and from any pub packages that
  are used (directly or indirectly) by the application.

It's TODONE

1. Use the primary color brightness to determine the color of the status bar.
    The status bar overlaps the toolbar, which has the primary color.
 2. Use Roboto for text.

This patch addresses late-breaking comments on previous patches.

They're actually leading values rather than line height values, which means
they're operative between paragraphs not within a given paragraph.

As part of this:
 - A lot of classes got new lerp functions, including e.g. TextStyle.
 - Theme's constructor story got overhauled. You can now configure
   everything if you really want to, and we're better about defaults.
 - Material no longer automatically animates its background color.
   (It still does for its shadow.)
 - Tabs try to get the indicator color from the theme.
 - The fields in ThemeData got reordered for sanity.
 - Theme.== and Theme.hashCode got fixed.
 - Typography got a bit of a spring cleaning.

Fixes #613.

Now with fewer lists.

Now TextStyle has a boolean "inherit" value, which controls whether null values
should use should inherit from the current default text style or whether they
should use their initial values.

The goal is to follow the guidelines in
https://github.com/flutter/engine/blob/master/sky/specs/style-guide.md#packages

Fixes #1638