I just noticed that the Dart files in Firebase Crashlytics Android reports from Flutter have .java file endings. It is a bit confusing, but I can confirm that these ".java" files are actually the Dart files in my project, i.e. the line numbers match up with what I have in them.
However, the file names are always <Dart class name>.java. For example:

GestureRecognizer.invokeCallback (GestureRecognizer.java:182)
TapGestureRecognizer.handleTapUp (TapGestureRecognizer.java:486)
BaseTapGestureRecognizer._checkUp (BaseTapGestureRecognizer.java:282)

The Dart files are not named after the classes and definitely do not have a .java file extension.

I am not exactly sure why this happens looking at the implementation.

(Moved from flutter/flutter#38718)