* Fix TODO syntax.
* Clarify messages for some timeouts, to aid debugging.
* Increase some other timeouts that were a needlessly short, to reduce sources of flakes.
* Remove some more timeouts that were mostly redundant, to remove complexity.
* Minor style cleanup.
* Remove some dangerous traps (specifically, hide the explicit start/end times in TimedEvent since they shouldn't matter).
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 6c56bb2. (#18362)
This reverts commit 3daebd0. (#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.
* Roll engine to b6df7a637498ca9beda1fa9cd7210e3202ea599f.
Changes since last roll:
```
b6df7a637 Roll dart to 290c576264faa096a0b3206c71b2435309d9f904. (#4771)
a6764dbd5 Add sources for Fuchsia target. (#4763)
2d5900615 [fuchsia] Remove unused header file. (#4769)
9717063b7 Revert "Roll dart to c080951d45e79cd25df98036c4be835b284a269c. (#4767)" (#4768)
9a9814312 Roll dart to c080951d45e79cd25df98036c4be835b284a269c. (#4767)
e74e8b35c [async] Update includes of async headers to new path (#4760)
e2c4b2760 Use Dart 2 camel case constants in the engine Dart libraries (#4766)
9c1e48434 Updates for Fuchsia roll. (#4765)
14c940e27 Switch from fxl::Mutex to std::mutex (#4764)
debf82c0b Roll Garnet (#4759)
5bffdefbb Use weak pointers to the accesibility bridge from objects vended to the UIKit accessibility framework. (#4761)
```
Greg Spencer
Jonah Williams
Devon Carew
Ian Hickson
Dan Field
Alexandre Ardhuin
Todd Volkert
Chris Bracken
Alexander Aprelev