* globalToLocal was just broken when there was a rotation and a
translation at the same time. This fixes that and adds a test.
* update graphic used by spinning_mixed since the old one went 404.
* simplify some of the code in the demo.
* fix MatrixUtils.transformPoint to be consistent with how we transform
points elsewhere.
* stop transforming points elsewhere, just use
MatrixUtils.transformPoint.
* make the Widget binding handle not having a root element.
* make the spinning_mixed demo update its widget tree.
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.
Turns out a common use for Baseline is making sure that the child's
baseline is higher than it otherwise would be, e.g. with the Material
font or other symbols.
Use the same technique for updating compositing bits as layout and
painting. This avoids walking the entire rendering tree when all you
need to update is a small subtree.
