This updates the visual look of the Chip class, so that it scales properly in the face of text scale (and label widget size) changes, and bases its height off of the label widget's height, constraining the other widgets it contains to be the same height.

To do this properly, I had to implement a custom render object that will measure the height of the label, so the guts of this class are basically rewritten.

In addition, to allow the circle avatar to increase in size when the chip does, I added minRadius and maxRadius arguments to it, and I updated its color handling to use the light/dark primary colors of the theme in a smart way instead of just using black and white.

Updated and added tests.

This attempts to apply some of what we learnt from UX studies, namely
that people wonder how to add multiple children to widget that take
one child.

Fixes #12480

* Allow FloatingActionButton to not have a heroTag.
* Allow FloatingActionButton to not have a child.
* Allow Tooltip to not have a child.
* Improve the debug output of the default FloatingActionButton hero tag.
* Improve the error message in the Hero clashing-tag case.
* Improve the debug output of the Hero widget.
* Improve the debug output of gesture-related widgets.
* Minor improvements to documentation.
* Fix some typos in comments.
* Fix some style nits.

Most of the framework widgets should work in terms of EdgeInsetsGeometry
rather than EdgeInsets so that their clients can supply directional
insets.

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.

Add Diagnosticable base class and documentation

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

* Provide haptic/acoustic feedback for tap & long-press on Android

* review comments

* fixed example code

* review comments

* comment fix

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

* more widget const constructors

* prefer const constructors

* address review comments

* make @immutable const

* fix build

* 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

Rename State.config to State.widget
Rename State.didUpdateConfig to State.didUpdateWidget
Renamed all State subclasses' local variables named config to something else

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

* address review comments

Covers lib/ in package:flutter.

We were trying to update the tooltip overlay entry, but that cannot work
because the overlay entry might have already built. Instead, we keep the
old value.

Fixes #7151

Also eliminate unused accentColor-related properties.

Use the typography specified in the theme rather than Typography.white.

This requires all AnimationController objects to be given a
TickerProvider, a class that can create the Ticker.

It also provides some nice mixins for people who want to have their
State provide a TickerProvider. And a schedulerTickerProvider for those
cases where you just want to see your battery burn.

Also, we now enforce destruction order for elements.

Renames stretch constructor to fill for better consistency with
the rest of the framework.

Fixes #5835.

Fixes #5393.

* Added custom radii to RRect.

This is the first commit towads an implementation of
MergeableMaterial. It adds custom radii to RRect.

* Renamed RRect constructors and added BorderRadius.

BorderRadius is a class similar to EdgeInsets that lets you define
all rounded corners of a rounded rectangle easily.

We were stacking up two dismiss timers. Now we don't start a new timer
if we've already got one. Also, fix an animation leak caught by the
test.

Fixes #4640

As requested by the material design team.

Fixes #4182

Also, remove several unused configuration options and fix an animation
leak.

We had a math-o.

Fixes #3563

Also fill in some related dartdocs.

Fix typo in Tooltip's shouldRelayout method.

This patch adds a consistent, simple description for the common pattern of
having a single child widget.