[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.
* Update project.pbxproj files to say Flutter rather than Chromium
Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.
* Update the copyright notice checker to require a standard notice on all files
* Update copyrights on Dart files. (This was a mechanical commit.)
* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.
Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).
* Clean up the copyrights in non-Dart files. (Manual edits.)
Also, make sure templates don't have copyrights.
* Fix some more ORGANIZATIONNAMEs
