* Roll to Dart SDK `1.20.0-dev.5.0`.

* bumps to `1.20.0-dev.5.0`.
* updates `analyzer` API use.

* Add explicit types.

Fixes #5835.

Fixes https://github.com/flutter/flutter/issues/5775

Added a widget that gives fine control over the use of steppers.
At any single moment, one step is shown with it own controls and
content.

Previously, flexible children were always required to fill their allocated
space. After this change, they can fit loosely into that space and not fill it.
When that happens, the remaining free space is allocated according to the
maixAxisAlignment.

Fixes #5858

Due to a synchronization issue, a PR was merged with a green build
that was supposed to be rebuilt and to fail. This commit fixes the
issue by renaming the usage of a constant.

* Update tools to use `analyzer` from vended Dart SDK.

* updates `flutter_tools` and `flutter_test` to use the SDK-vended `analyzer` package
* tweaks dependency tracking logic to only record the SDK-vended `analyzer` so as not to crash on spurious conflicts (due to transitive dependencies)

* Review fixes.

Fixes #4713.

Fixes https://github.com/flutter/flutter/issues/5684

* refactor _run to runCmd

* replace requiresProjectRoot getter with call to commandValidator

* replace requiresDevice getter with call to findTargetDevice

* trace command requires a debug connection, not a device

* inline androidOnly getter

* rename command methods to verifyTheRunCmd and runCmd

* move common verification into BuildSubCommand

* rename deviceForCommand to device

* rename methods to verifyThenRunCommand and runCommand

As per our style guide, if you can't explain something, refactor it. I
studied this function for a while and still can't explain it, so...

Fixes #5872

See #4434.

Fixes #3208.

Fixes #4618.

Renamed expansion_panels.dart to expansion_panel.dart.

Changed drawer header to use theme's divider color.

Having this base class lets classes like CustomPainter and DataTableSource be
more agnostic as to what's generating the repaints.

The engine now reports coordinates in physical pixels.

Also, make ProxyWidget and ProxyElement public.

Fixes #4505

This moves all of the various .analysis_options* files to the flutter repo root so that it's easier to
* remember to keep them all in sync, and
* easily refer customers to them

Also, fix an old TODO, and add a test of various things on TextStyle.

...requires an engine roll to pick up https://github.com/flutter/engine/pull/3025 and https://github.com/flutter/engine/pull/3027.

Fixes https://github.com/flutter/flutter/issues/5840

Moves BorderRadius to above its first use.
Slight improvements to the BoxShape docs.

Changed MergableMaterial to animated between states that have dividers
and those that don't in order not to have dividers that appear
unanimatedly. Fixes #5847.

* Added OverscrollIndicatorEdge et al

* RefreshIndicator only clamps its scrollable edge

* added a test

* Updated the test

* fixed lint-os

* fixed a typo

* Scrollable should restore its viewport dimensions when it reappears

* removed an accidental commit

* updated per review feedback

part of https://github.com/flutter/flutter/issues/5789

The deprecation period has ended and we believe its clients have migrated to
other solutions.

Fixes #2205