- Create a FlutterErrorDetails struct-like class that describes an
exception along with more details that aren't in the exception, like
where it was caught and what was going on when it was caught.
- Provide a FlutterError static API for handling these objects:
- FlutterError.onError which is called whenever Flutter catches an
error.
- FlutterError.reportError() which handles an error.
- FlutterError.dumpErrorToConsole() which is the default behavior
for onError.
- Removes all the existing exception handler callbacks.
- Replaces all the existing places that described exceptions using
debugPrint with calls to FlutterError.reportError().
- Extend lockState() to also catch exceptions, so that we catch
exceptions that happen during finalizers.
- Make the test framework catch errors and treat them as failures.
- Provide a mechanism to override this behavior in the test framework.
- Make the tests that used to depend on the exception handler
callbacks use this new mechanism.
- Make pump() also support the phase argument.
- Improve some tests using these new features.
Fixes#2356, #2988, #2985, #2220.
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