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.

This modifies the MaterialButton to expand vertically to fit the size of the contained child, no matter what the child widget is. It tries to be as close as possible to the minHeight constraint.

Also updated some doc comments to have headers (extra blank line after first sentence), and to wrap at 80 cols.

Addresses #12311

backgroundColor -> color
backgroundImage -> image
BackgroundImage -> DecorationImage

* comprehensive list of lints
* add comments to commented out lint
* fix unnecessary_this lints
* exclude prefer_final_fields

* Manually fix every use of Point.x and Point.y

Some of these were moved to dx/dy, but not all.

* Manually convert uses of the old gradient API

* Remove old reference to Point.

* Mechanical changes

I applied the following at the root of the Flutter repository:

git ls-files -z | xargs -0 sed -i 's/\bPoint[.]origin\b/Offset.zero/g'
git ls-files -z | xargs -0 sed -i 's/\bPoint[.]lerp\b/Offset.lerp/g'
git ls-files -z | xargs -0 sed -i 's/\bnew Point\b/new Offset/g'
git ls-files -z | xargs -0 sed -i 's/\bconst Point\b/const Offset/g'
git ls-files -z | xargs -0 sed -i 's/\bstatic Point /static Offset /g'
git ls-files -z | xargs -0 sed -i 's/\bfinal Point /final Offset /g'
git ls-files -z | xargs -0 sed -i 's/^\( *\)Point /\1Offset /g'
git ls-files -z | xargs -0 sed -i 's/ui[.]Point\b/ui.Offset/g'
git ls-files -z | xargs -0 sed -i 's/(Point\b/(Offset/g'
git ls-files -z | xargs -0 sed -i 's/\([[{,]\) Point\b/\1 Offset/g'
git ls-files -z | xargs -0 sed -i 's/@required Point\b/@required Offset/g'
git ls-files -z | xargs -0 sed -i 's/<Point>/<Offset>/g'
git ls-files -z | xargs -0 sed -i 's/[.]toOffset()//g'
git ls-files -z | xargs -0 sed -i 's/[.]toPoint()//g'
git ls-files -z | xargs -0 sed -i 's/\bshow Point, /show /g'
git ls-files -z | xargs -0 sed -i 's/\bshow Point;/show Offset;/g'

* Mechanical changes - dartdocs

I applied the following at the root of the Flutter repository:

git ls-files -z | xargs -0 sed -i 's/\ba \[Point\]/an [Offset]/g'
git ls-files -z | xargs -0 sed -i 's/\[Point\]/[Offset]/g'

* Further improvements and a test

* Fix minor errors from rebasing...

* Roll engine

This yak shave went as follows:

Fix https://github.com/flutter/flutter/issues/8795 by adding stocks to
the examples README.

Notice the layers entry in that README isn't quite right either.
Update that.

Check the layers/README file is worth pointing at.

Update the layers/README.

Let's run some of the layer tests to see if they still work.

Oops, need to update them to gradle.

Ok let's try running them again.

Oops, sector is broken.

Add a test for sector.

Fix sector. Find you need to add an assert to a const constructor.

Notice we need to turn const asserts on for the analyzer.

Notice the analysis_options files are out of sync with each other and
with the full list of lints.

Turn on the lints that should be on.

Fix the bugs that finds.

Also, make sure that the parent is notified when they change.

Fixes #2298

It's safe to remove the unneeded `void`s from setters since the blocking issues in the
`always_declare_return_types` lint have been fixed (https://github.com/dart-lang/linter/).  We can also safely flip the bit on  `avoid_return_types_on_setters`.

This also shrinks the width of the error messages a bit because now that
we use 'package:' URLs the stacks are a bit narrower.

I ran into a case where I was setting minHeight=∞ and then calling
layout() with that constraint, which is all kinds of bad. To try to
catch this earlier, this patch now provides a way to catch constraints
that are requiring infinite values.

We don't _always_ check this because there are valid uses for
BoxConstraints.biggest, e.g. as an additionalConstraint.

Our examples have been growing organically over time. This patch cleans
them up to illustrate specific aspects of Flutter.