...and various other minor cleanup:
* Moved "FLUTTER_STORAGE_BASE_URL" into a constant throughout the code. There are other strings that we should do that to but this one was relevant to the code I was changing.
* Fixed the logger's handling of slow warnings. Previously it deleted too much text. Fixed the test for that to actually verify it entirely, too.
* Made the logger delete the slow warning when it's finished.
* Fixed 'Please choose one (To quit, press "q/Q")' message to be the cleaner 'Please choose one (or "q" to quit)'.
* Added a debug toString to ValidationResult for debugging purposes (not used).
* In http_host_validator:
- Shortened constant names to be clearer (e.g. kPubDevHttpHost -> kPubDev).
- Added GitHub as a tested host since when you run `flutter` we hit that immediately.
- Renamed the check "Network resources".
- Updated the `slowWarning` of the check to say which hosts are pending.
- Removed all timeout logic. Timeouts violate our style guide.
- Removed `int.parse(... ?? '10')`; passing a constant to `int.parse` is inefficient.
- Replaced the `_HostValidationResult` class with `String?` for simplicity.
- Improved the error messages to be more detailed.
- Removed all checks that dependened on the stringification of exceptions. That's very brittle.
- Added a warning specifically for HandshakeException that talks about the implications (MITM attacks).
- Replaced exception-message-parsing logic with just calling `Uri.tryParse` and validating the result.
- Replaced a lot of list-filtering logic with just a single for loop to check the results.
- Replaced code that added a constant to a known-empty list with just returning a constant list.
- Revamped the logic for deciding which hosts to check to just use a single chain of if/else blocks instead of getters, lists literals with `if` expressions, `??`, functions, etc spread over multiple places in the code.
[flutter tools] Add a DelegatingLogger class
Move most of `DelegateLogger` `from test/src/testbed.dart` to
`lib/src/base/logger.dart` to better formalize the common practice of
chaining `Logger`s together. I renamed the class since it isn't
itself the delegate and to better match the `Delegating...` classes
from `package:collection`.
Additionally, add a freestanding `asLogger<T>` function to "cast" a
`Logger` into a matching delegate if possible. This will allow
`Logger` chains to be ordered a *bit* more freely (e.g.
`NotifyingLogger` and `AppRunLogger` will no longer required to be
at the end of the chain, an unwritten rule that has led to breakage in
google3). Chain order still matters since lack of virtual dispatch
means that parent `Logger`s can never invoke child methods, however.
I made `asLogger<T>` a freestanding function because I didn't want to
make it part of the `Logger` interface (and I thought that making it
an extension method might be weird).
Bonus cleanup:
There no longer appears to be a way to construct an `AppRunLogger`
with a null parent, so remove all of code paths for that case and
make the `parent` construction parameter required.
We have too many loggers, and the logger construction rules are too complicated to be untested. Capture these in a LoggerFactory and test that construction is correct.
