The code was attempting to delete temporaryDirectory while it should have been deleting tempBundleDirectory

* Default to strong for 'flutter test --preview-dart-2' mode

* Remove empty line

* Dont init to null

* Break up line to make it more readable

* Add missing type annotation

This is in attempt to resolve build failure on Windows.

Increase coverage collection timeout to 2 minutes. Leafy is hitting the limits of the previous timeout of 30 seconds for tests that touch a lot of code in the app. (#13527)

* enable lint prefer_asserts_in_initializer_lists

* enable --assert-initializer

* round 3

* partially address comments

* merge

* review notes

* review

* review

* review

* Quiet debug test runner output when in machine mode.

See: https://github.com/flutter/flutter-intellij/issues/1176

* json => machine

This adds a way to run only a subset of the tests.
(The new flags do the same thing as 'pub run test'.)

The main purpose of this PR is to make it so that when you set the
initial route and it's a hierarchical route (e.g. `/a/b/c`), it
implies multiple pushes, one for each step of the route (so in that
case, `/`, `/a`, `/a/b`, and `/a/b/c`, in that order). If any of those
routes don't exist, it falls back to '/'.

As part of doing that, I:

 * Changed the default for MaterialApp.initialRoute to honor the
   actual initial route.

 * Added a MaterialApp.onUnknownRoute for handling bad routes.

 * Added a feature to flutter_driver that allows the host test script
   and the device test app to communicate.

 * Added a test to make sure `flutter drive --route` works.
   (Hopefully that will also prove `flutter run --route` works, though
   this isn't testing the `flutter` tool's side of that. My main
   concern is over whether the engine side works.)

 * Fixed `flutter drive` to output the right target file name.

 * Changed how the stocks app represents its data, so that we can
   show a page for a stock before we know if it exists.

 * Made it possible to show a stock page that doesn't exist. It shows
   a progress indicator if we're loading the data, or else shows a
   message saying it doesn't exist.

 * Changed the pathing structure of routes in stocks to work more
   sanely.

 * Made search in the stocks app actually work (before it only worked
   if we happened to accidentally trigger a rebuild). Added a test.

 * Replaced some custom code in the stocks app with a BackButton.

 * Added a "color" feature to BackButton to support the stocks use case.

 * Spaced out the ErrorWidget text a bit more.

 * Added `RouteSettings.copyWith`, which I ended up not using.

 * Improved the error messages around routing.

While I was in some files I made a few formatting fixes, fixed some
code health issues, and also removed `flaky: true` from some devicelab
tests that have been stable for a while. Also added some documentation
here and there.

(The Flutter plugin will use this to update the UI with test progress.)

- remove unused collector parameter
- clarify a comment
- inline _currentPackageTestDir

And add comments explaining why.

Currently this just prints the observatory URL as a JSON event.
Refactored the code to make this fit in.

Builds on engine fixes to #9813

Also fixes #7366

This reverts commit 9f5fa31e.

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

* address review comments

* Bump to Dart SDK 1.23.0-dev.10

* allows us to understand flutter usage via telemetry
* brings in `@immutable`

Fixes: #9042

* completer fix

* Update to platform 1.1.1.

This assumes a fix to https://github.com/dart-lang/test/issues/542

The timeout added in this patch is a workaround for https://github.com/dart-lang/coverage/issues/165

* Small Flutter strong mode cleanup fixes.

These are cases where strong mode down cast composite errors
generally indicated cases that would performance or correctness
issues if Flutter code was run in a strong mode VM.

* Fix Command API so that it is always in terms of Map<String,String>.

* Fix typedef

Make debugging tests in a debugger easier.

Fixes https://github.com/flutter/flutter/issues/163

...now that we have generic methods, their types need to be specified too.

This brings the feature back, since removing it broke one of our more
exotic sets of customers.