* address unused element issues and new warnings

* add a missing return

* enable lint prefer_asserts_in_initializer_lists

* enable --assert-initializer

* a => an

(I suspect this accounts the sets of microtasks from scheduleWarmUpFrame now running separately.)

Issue https://github.com/flutter/flutter/issues/9998

* Surface shadowColor from RenderPhysicalModel to Material

* Fix typo in material_test

* Add nullability info to documentation

* Add support for animating elevation shadow color

* Add shadowColor to Material's debugFillProperties()

* Add missing default value for elevation in Material debugFillProperties()

* Add missing non-null asserts for animate flags in AnimatedPhysicalModel

* Add test for shadow color animating smoothly

* delay taking screenshot to allow GPU thread to render the frame

* address comments

Since MethodCall equality checks are limited to test scenarios, this
patch replaces them with an equivalent test matcher. At present
MethodCalls are always used in scenarios where indentity-based
equality/hashing is appropriate.

This change avoids an assertion failure when MethodCall args are
Iterable (possible since args are of type dyanmic), and hashValue() from
dart:ui asserts that its input is not an Iterable.

The alternative of implementing support for deep equality in dart:ui was
rejected on the basis that if we're to encourage performant code,
expensive checks should be obviously-expensive to the author.

There was a left-bias when MainAxisSize.min couldn't be honoured.

* Leave a version tag when creating project

* Generalize .version to .metadata

Use TextPainter.preferredLineHeight to estimate line height for Cupertino selection handles (#12833)

Fixes https://github.com/flutter/flutter/issues/12046

* Built first tab

* Small additions

* started tab 3

* Need color arithmetics

* tab 2 built

* finalize

* lint and tests

* review

* Reapply docs after rebase

* use color.computeLuminance

* linter

* nit

* remove extracted methods

* lint

* make microbenchmark logging verbose

* prefix JSON so it can be parsed in verbose mode

This fixes the assumption that InputDecorator had where it expected baseStyle to be a complete style. Now it merges the baseStyle with the subhead style instead of substituting it entirely.

This fixes #12832.

* Identify text fields as such to a11y

* focus

* make travis happy

* review comments

Adds `Scaffold#endDrawer` property to supply a second drawer to a Scaffold.

In order to allow chips to be properly drawn when they expand in size (without
using IntrinsicHeight), I needed a BoxDecoration shape that would be dependent
upon the rendered height of the widget. This seemed to be pretty generally
useful, so I added a new ShapeDecoration called StadiumBorder. It uses the
minimum dimension to adjust the BorderRadius of a rounded rect in the shape
decoration.

I also converted some uses of BoxShape to be case statements, updated the
chips to use the StadiumBorder decoration, and updated some of the metrics to match
the Material spec, as well as implementing lerping to and from StadiumBorder.