* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

- Check memory usage in release builds, not profile.
- Use multiple runs and average the results.

* Revert "Add pub cache, artifacts, pkgs to Cirrus cache (#20080)"

This reverts commit 07e93b38.

* Revert "Reduce noise on the memory benchmarks (#19630)"

This reverts commit 8eb5cb7d.

- Check memory usage in release builds, not profile.
- Use multiple runs and average the results.

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.

Revert "Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) again (#19277)" (#19295)" (#19322)

This reverts commit cc122f16.

Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) again (#19277)" (#19295)

This reverts commit 700cb767 as it
breaks Windows tests.

* Revert "Revert "Roll engine to fed2ea458ed49088d33eddabc546ba56d600c717 (includes dart roll) (#19044)" (#19276)"

This reverts commit cf932490 as it also
includes fix for type error that broke tests.

* Add type cast for dart2 type checks.

* Move up to latest goldens

* Make inDirectory() type-parameterized.

* Add typecasting to transitions_perf_test.dart and microbenchmarks.

* Add boolean flag initialization in save_catalog_screenshots.dart

* Add type conversion to gallery transition test

On smaller-screen devices such as the iPhone 4s, more scrolling is
required between the Material dialog demo and the Material pickers demo
than will happen within the default timeout.

This reverts commit 1095eafe.

When attempting to locate an element in the Flutter Gallery transition
performance driver test, attempt to scroll downward in increments of 25%
of the screen rather than by an absolute pixel amount.

This helps get the test passing on devices with relatively small screen
heights.

Revert longPress/Tap and Gallery changes

* Revert "New Flutter Gallery UI (#16936)"

This reverts commit 7038597b.

A new front-end for the Flutter Gallery example.

* Gallery scaffolding

* Started RenderSliver

* demo and initial hookup

* Cleaned up demo more and scaffolding basic sliver->widget communication structure.

* works

* states and default indicator building works

* start adding docs

* added an alignment setting optimized the sliver relayout mechanism

* tested a default bottom aligned sized indicator

* Added a bunch of tests

* more fixes and more tests

* Finished the tests

* Add docs

* Add more doc diffing wrt material pull to refresh

* Mention nav bar synergy

* add more asserts

* review 1

* Fix mockito 2 / dart 2 / strong typed tests

* review

* Remove the vscode config

* review

* 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

* controller, position and test

* Make controllers swappable

* WIP

* Create a ListWheelScrollPhysics

* Created picker and gallery demo and testing now

* Works. Ready to document and test.

* Document and add tests. Make the scroll controller more generic.

* minor cleanup

* review

* review

* fix tests

* stop using TransformLayers for now

In https://github.com/flutter/flutter/pull/13141 I updated the demo name
from 'Animated Images' to 'Animated images' before submitted, but did
not update the name in the smoketest and transitions_perf test.

* 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

package:test does not allow main() methods to have required
arguments - changing to an optional positional arguments list
fixes this.

* Benchmark for semantic overhead during transitions

* review comments

Also refactors demos list into a class with `synchronized` and
`profiled` properties.

When run with --trace-startup, as we do in this test, the VM stores
trace events in an endless buffer instead of a ring buffer. To avoid
out-of-memory conditions, we restrict timeline collection to a subset.