Cirrus CI has macOS VMs, so this turns on an instance for tests so that we can evaluate if we can use Cirrus for all three platforms or not.

Makes them all be generated on Linux and fixes some to not be so large.

Bug: https://github.com/flutter/flutter/issues/19435

Bug: https://github.com/flutter/flutter/issues/19494

Fixes https://github.com/flutter/flutter/issues/19465

This reverts commit b0eb1632.

This reverts commit cc1cf13e.

* Chevrons in month picker are semi-transparent when the month is scrolled

* Added type missing annotation

This reverts commit 57d78cc7.

This reverts commit 44995dc4.

This uses @kevmoo's completion package to do command line completion for flutter, and a new command "bash-completion" (with alias "zsh-completion") that will output the necessary shell script setup code, and adds the hidden command "completion" that does the actual completion.

Because it adds a dependency, I also had to do flutter update-packages --force-upgrade.

Fixes #18988.

This reverts commit e22f9974.

Adding the exit(exitCode) fixes the hang.
Tested by running `fx run-host-tests` with a topaz checkout.
Verified the hang before, no hang after.

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

This reverts commit cc122f16.

This reverts commit 032f8cdb.

The test runner hangs on exit after all tests pass when trying
to roll this into Fuchsia.

* Preserve original kernel file for isolate spawn requests.

This change gives incremental kernel files ".incremental.dill" extension thereby preserving original kernel file.

Bug: https://github.com/flutter/flutter/issues/16084
Bug: https://github.com/flutter/flutter/issues/17012
Bug: https://github.com/flutter/flutter/issues/17983

* Factor out naming logic into separate function

* Fix string vs uri

* Allow a longer timeout for app launches

* Include timings in errors when waiting for events

* Extract a helper that adds a timeout and includes message logging

* Ensure all timeouts include messages

* Ensure logs are set up before we invoke actions

* Ensure all messages are logged during timeout periods

This adds a new stream _allMessages that collects all output (as routed through debugPrint) and updates _timeoutWithMessages to use that instead of stdin/out of only the flutter run process (since that was missing stdin - the sends, and both input/output to the VM service).

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

ios-deploy relies on LLDB.framework, which relies on /usr/bin/python and
the 'six' module that's installed on the system. However, it appears to
use the first version of Python on PATH, rather than explicitly
specifying the system install.  If a user has a custom install of Python
(e.g., via Homebrew or MacPorts) ahead of the system Python on their
PATH, LLDB.framework will pick up that version instead. If the user
hasn't installed the 'six' module, ios-deploy will fail with a
relatively cryptic error message.

This patch pushes /usr/bin to the front of PATH for the duration of the
ios-deploy run to avoid this scenario.

This patch also removes checks for package six.

Neither Flutter nor any of its direct dependencies/tooling relies on
package six. ios-deploy depends on LLDB.framework (included with Xcode),
which relies on a Python script that imports this package but uses
whichever Python is at the front of the path. Flutter now invokes
ios-deploy with a PATH with /usr/bin forced to the front in order to
avoid this problem.

We could have retained the check out of paranoia, but this seems
unnecessary since it's entirely possible LLDB.framework may one day drop
this dependency, in which case I'd expect the base system install of
Python would likely drop it as well.

* Fixed codesign error message width

* Fixed mac_test

* Removed snackbar code

All slivers must start with Sliver (or CupertinoSliver).
All widgets must have a key argument.

Also, some minor tweaks here and there to style and docs.