* Remove the workaround that pinned args to v0.13.6
This reverts most of the changes in commit 6331b6c8
* throw exception if exit code is not an integer
* rework command infrastructure to throw ToolExit when non-zero exitCode
* convert commands to return Future<Null>
* cleanup remaining commands to use throwToolExit for non-zero exit code
* remove isUnusual exception message
* add type annotations for updated args package

Switch our pubspec.yamls to using SDK sources so that we can have consistent
source types when we depend on these packages from external packages using SDK
sources.

* suppress warning; decouple the analyzer versions

* also pass in --no-packages-dir

* 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.

* Udpate to Dart `1.20.0-dev.1.0`.

Udpate to Dart `1.20.0-dev.1.0` and corresponding `analyzer` package.

* Added `--no-packages-dir`.

* Revert extension to master.

* Added ignores.

* Review nits.

* More nits.

Last dev push for `1.18`.

Bye-bye `@protected `trampolines! :)

* brings in analyzer version (`0.27.4-alpha.14`) corresponding to current Dart SDK (`1.18.0-dev.2.0`).
* updates analysis to use prefered API for embedder URI resolution
* adds trampolines to `State` and `StatelessWidget` to allow for warning-free within-library @protected access (needed since we closed off access to @protected closures from outside subclasses).
* turns off cache dependency tracking for analysis (in DDC this amounted to a 10% speed improvement).

* bump out dep on the test package

* add other pubspecs

Update analyzer dep to 0.27.4-alpha.9 to enjoy analyzer perf improvements (https://codereview.chromium.org/2011183004/) (and keep in sync with the SDK).

(This is a revisit to https://github.com/flutter/flutter/pull/4253.)

Notably, this will allow us to play with

* the fixed `public_member_api_docs` that now checks for documented getters when checking setters (https://github.com/dart-lang/linter/issues/237), and
* the new `comment_references` lint that ensures identifiers referenced in docs are in scope (https://github.com/dart-lang/linter/issues/240).

This reverts commit f91cf1c4.

Notably, this will allow us to play with

* the fixed `public_member_api_docs` that now checks for documented getters when checking setters (https://github.com/dart-lang/linter/issues/237), and
* the new `comment_references` lint that ensures identifiers referenced in docs are in scope (https://github.com/dart-lang/linter/issues/240).

Introduces a new Dart analysis wrapper that works directly with the analyzer API (in favor of shelling out to a separate process).

Some consequences:

  * we no longer need to fear parts (simplifying our dart file gathering)
  * we can filter by error code (when needed), rather than by error strings
  * no more IO scraping
  * no need to generate `main()` or to run with `--package-warnings`
  * we now specify an analyzer (and linter) version in the pubspec (we’ll want to make sure this doesn’t diverge too far from the analyzer shipped with the SDK but it does give us some room to play with experimental builds)
  * no more (re)scanning of error source files (and so no more source cache)
  * should generally be a bit simpler and easier to maintain
  * runs a bit faster :)

We need to pin the version of package:analyzer we use to avoid version skew
within our project.

The mojo_sdk has cleaned up its dependencies, so we no longer need to depend on
package:test from package:flutter.

This patch switches us from using our previous hacking approach to integrating
with package:test to using the new PlatformPlugin interface.

We use a number of non-public APIs in the test package, which makes our
dependency quite fragile. This patch pins a specific, known-good version. We
should update to the lastest version in a follow-up patch.

This package contains WidgetTester, which is very useful when writing tests for
widgets.