* Remove stray extra space

* Add ImageStreamCompleter.hasListeners (and cleanup)

This is mostly just some cleanup of stuff I ran into, but it makes
`hasListeners` protected on `ImageStreamCompleter`, because otherwise
there's no way to track if listeners are registered or not.

* Address review comments

We have templates now.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

fuchsia_tester.dart still assumes Dart 1. Previously, it ran tests directly
from source, flutter_platform.dart automatically runs a kernel compile when
operating in Dart 2 mode, but this assumes a functional Dart SDK is available
in the artifacts directly, and fuchsia_tester.dart mocks out the artifacts
directory with an empty temp dir.

Remaining work is:
1. Get the frontend server building as a dependency on Fuchsia.
2. Patch fuchsia_tester.dart to use a valid Dart SDK and frontend server.

This also reverts migration to Dart 2 typedef syntax.

This reverts commit 6c56bb24. (#18362)
This reverts commit 3daebd05. (#18316)

Now that Dart 1 is turned off, reapplying my change to turn on the prefer_generic_function_type_aliases analysis option, and fix all the typedefs to Dart 2 preferred syntax.

Also eliminated the unused analysis_options_repo.yaml file and turned on public_member_api_docs in analysys_options.yaml.

No logic changes, just changing the typedef syntax for all typedefs, and updating analysis options.

Revert "Update typedef syntax to use Function notation and turn on lint for old notation. (#18035)" (#18041)

This reverts commit 32586020.

Fixes #18028

Just changes typedef declarations, no logic changes.

Seems like we don't yet run the flutter tests on Windows, but we're
close to being able to. This makes some minor changes to make that
more possible:

 - fix the stack parsing code to support Windows paths
 - fix the tests for the stack error handling code to handle Windows paths
 - skip some tests that rely on Ahem font metrics

Fixes https://github.com/flutter/flutter/issues/10695

This reverts commit e7061698.

This causes preview-dart-2 test failures.

* Roll engine

* Move assert requiring 'this' from initializer to constructor body

* Update test expected message

* Relax regexp to allow wider array of dart uris

Also:

 * Provide a better message when you lerp from infinity to finity
   constraints.

 * Make the striped marker support RTL.

 * By popular demand, dump a warning to the console the first time
   a particular Flex overflows. (Resets on hot reload.)

Also includes minor doc fixes.

* enable lint overridden_fields

* address review comment

Covers lib/ in package:flutter.

See https://github.com/dart-lang/sdk/issues/28463, which I think is a
regression.

This also fixes the regression introduced by
https://codereview.chromium.org/2559773002 whereby we were no longer
checking any of the lints.

* MultiTapGestureRecognizer previously would assert if there was no
   competition.
 * GestureArenaTeam would always select the first recongizer as the
   winner even if a later recognizer actually accepted the pointer
   sequence.
 * debugPrintStack would fail a type check if maxFrames was non-null.
 * FractionalOffset.lerp would throw a null-pointer exception if its
   second argument was null.

Also, add a number of tests for previously untested lines of code.

Previously, pumpWidget() would do a partial pump (it didn't trigger
Ticker callbacks or post-frame callbacks), and pump() would do a full
pump. This patch brings them closer together. It also makes runApp run a
full actual frame, rather than skipping the transient callback part of
the frame logic. Having "half-frames" in the system was confusing and
could lead to bugs where code expecting to run before the next layout
pass didn't because a "half-frame" ran first.

Also, make Tickers start ticking in the frame that they were started in,
if they were started during a frame. This means we no longer spin a
frame for t=0, we jump straight to the first actual frame.

Other changes in this patch:

* rename WidgetsBinding._runApp to WidgetsBinding.attachRootWidget, so
  that tests can use it to more accurately mock out runApp.

* allow loadStructuredData to return synchronously.

* make handleBeginFrame handle not being given a time stamp.

* make DataPipeImageProvider.loadAsync protected (rather than private),
  and document it. There wasn't really a reason for it to be private.

* fix ImageConfiguration.toString.

* introduce debugPrintBuildScope and debugPrintScheduleBuildForStacks,
  which can help debug problems with widgets getting marked as dirty but
  not cleaned.

* make debugPrintRebuildDirtyWidgets say "Building" the first time and
  "Rebuilding" the second, to make it clearer when a widget is first
  created. This makes debugging widget lifecycle issues much easier.

* make debugDumpApp more resilient.

* debugPrintStack now takes a label that is printed before the stack.

* improve the banner shown for debugPrintBeginFrameBanner.

* various and sundry documentation fixes

Changes in this patch:
- iOS now uses a different scrollDrag constant than Android.
   - ScrollConfigurationDelegate now knows about target platforms.
   - ScrollBehaviors now know about target platforms.
   - RawInputLine now has to be told what platform it's targetting.
   - PageableList now has a concept of target platform.
- make debugPrintStack filter its stack.
   - move debugPrintStack to `assertions.dart`.
- add support for limiting the number of frames to debugPrintStack.
- make defaultTargetPlatform default to android in test environments.
- remove OverscrollStyle and MaterialApp's overscrollStyle argument. You
  can now control the overscroll style using Theme.platform.
- the default scroll configuration is now private to avoid people
  relying on the defaultTargetPlatform getter in their subclasses (since
  they really should use Theme.of(context).platform).
- fix some typos I noticed in some tests.
- added a test for flinging scrollables, that checks that the behavior
  differs on the two target platforms.
- made flingFrom and fling in the test API pump the frames.
- added more docs to the test API.
- made the TestAsyncUtils.guard() method report uncaught errors to help
  debug errors when using that API.

Adds Scheduler.debugPrintTransientCallbackRegistrationStack so that you
can find out how your current callback got registered.

- show the next error fully after a hot reload
- hide _AssertionError in stacks
- immediately rebuild after a reassemble, so that hit tests work
- catch errors when notifying global key listeners

For consistency.

Fixes #4142

Don't suggest filing an issue when we can definitively say that the
assertion in question was not thrown from within the flutter package.
Fixes https://github.com/flutter/flutter/issues/3812.

Put the stack trace first after the message, with more details below the
stack trace, since the stack is often very useful and the stacks are no
longer stupidly long.

Better document the 'rescheduling' feature, and improve the error
handling asserts when it is misused.
Fixes https://github.com/flutter/flutter/issues/3888.

Improve the wording around the stack dump for exceptions during
callbacks.

Improve the color and font size of messages in live tests.
Fixes https://github.com/flutter/flutter/issues/4018.

This makes it possible to substitute 'flutter run' for 'flutter test'
and actually watch a test run on a device.

For any test that depends on flutter_test:

1. Remove any import of 'package:test/test.dart'.

2. Replace `testWidgets('...', (WidgetTester tester) {`
      with `testWidgets('...', (WidgetTester tester) async {`

3. Add an "await" in front of calls to any of the following:
    * tap()
    * tapAt()
    * fling()
    * flingFrom()
    * scroll()
    * scrollAt()
    * pump()
    * pumpWidget()

4. Replace any calls to `tester.flushMicrotasks()` with calls to
   `await tester.idle()`.

There's a guarding API that you can use, if you have particularly
complicated tests, to get better error messages. Search for
TestAsyncUtils.

* Refactor widget test framework

Instead of:

```dart
  test("Card Collection smoke test", () {
    testWidgets((WidgetTester tester) {
```

...you now say:

```dart
  testWidgets("Card Collection smoke test", (WidgetTester tester) {
```

Instead of:

```dart
  expect(tester, hasWidget(find.text('hello')));
```

...you now say:

```dart
  expect(find.text('hello'), findsOneWidget);
```

Instead of the previous API (exists, widgets, widget, stateOf,
elementOf, etc), you now have the following comprehensive API. All these
are functions that take a Finder, except the all* properties.

* `any()` - true if anything matches, c.f. `Iterable.any`
* `allWidgets` - all the widgets in the tree
* `widget()` - the one and only widget that matches the finder
* `firstWidget()` - the first widget that matches the finder
* `allElements` - all the elements in the tree
* `element()` - the one and only element that matches the finder
* `firstElement()` - the first element that matches the finder
* `allStates` - all the `State`s in the tree
* `state()` - the one and only state that matches the finder
* `firstState()` - the first state that matches the finder
* `allRenderObjects` - all the render objects in the tree
* `renderObject()` - the one and only render object that matches the finder
* `firstRenderObject()` - the first render object that matches the finder

There's also `layers' which returns the list of current layers.

`tap`, `fling`, getCenter, getSize, etc, take Finders, like the APIs
above, and expect there to only be one matching widget.

The finders are:

 * `find.text(String text)`
 * `find.widgetWithText(Type widgetType, String text)`
 * `find.byKey(Key key)`
 * `find.byType(Type type)`
 * `find.byElementType(Type type)`
 * `find.byConfig(Widget config)`
 * `find.byWidgetPredicate(WidgetPredicate predicate)`
 * `find.byElementPredicate(ElementPredicate predicate)`

The matchers (for `expect`) are:

 * `findsNothing`
 * `findsWidgets`
 * `findsOneWidget`
 * `findsNWidgets(n)`
 * `isOnStage`
 * `isOffStage`
 * `isInCard`
 * `isNotInCard`

Benchmarks now use benchmarkWidgets instead of testWidgets.

Also, for those of you using mockers, `serviceMocker` now automatically
handles the binding initialization.

This patch also:

* changes how tests are run so that we can more easily swap the logic
  out for a "real" mode instead of FakeAsync.

* introduces CachingIterable.

* changes how flutter_driver interacts with the widget tree to use the
  aforementioned new API rather than ElementTreeTester, which is gone.

* removes ElementTreeTester.

* changes the semantics of a test for scrollables because we couldn't
  convince ourselves that the old semantics made sense; it only worked
  before because flushing the microtasks after every event was broken.

* fixes the flushing of microtasks after every event.

* Reindent the tests

* Fix review comments

Fixes https://github.com/flutter/flutter/issues/3352

We're getting back to the point where we have a bunch of foundation APIs
and it's getting confusing having them mixed with services/.