Fix --debug

Clean up scroll behaviour.

Remove redundant Material from start project

This makes ScrollBehavior agnostic about the kind of scroll.
This also means ExtentScrollBehavior's comment about being linear is
more relevant (previously it was true of all scroll behaviours).

add a validator for Atom

...and some style nits.

Some trivial animation library cleanup.

more details in infra/README.md

"flutter create" can generate a basic driver test; "flutter drive" gains new options

"flutter create" adds option `--with-driver-test` that adds
dependencies to `flutter_driver` in `pubspec.yaml` and creates
a basic driver test runnable via `flutter drive
--target=test_driver/e2e.dart`

"flutter drive" new options:

- `--keep-app-running` tells the driver to not stop the app after tests
  are done
- `--use-existing-app` tells the driver to not start a new app but use
  an already running instance

fix a checked mode assertion

remove iosSimulator field from ApplicationPackageStore

log for specific adb devices

Address issues raised in PR #2047

Fix linter error regarding extra braces in string interpolation in devices.dart

Update status messages when unsupported devices are detected by the tools

check to see if the xcode eula has been signed

Remove ThemeData.primarySwatch

In the dark theme, there isn't really a primary swatch, so this API was
a sandtrap. Instead, be explicit about the colors we need for various
widgets in the theme.

Fixes #1277

Improve issue template

Fix link to bug-reports page. Also, hint at how to get the flutter
version.

Add TestGesture

This helper makes it easier to write correct tests that involve
gestures.

Fixes #1855

SnackBar should have a single optional action

Remove redundant material_ prefix

Animation status callbacks should be re-entrant

These files are already in the "material" folder. They don't need to be
prefixed with material again.

Fixes #702

add the ability to start and stop device polling

We should mutate the status of the AnimationController before calling
the status callbacks so that we're prepared to be re-entered.

Fixes #1911