We are experimenting with allowing asserts in initializer lists.
See the design document.

For this experiment, we need (behind the flag --assert-initializer):

• the VM to implement the assertions (Committed: 99439a3)
• the analyzer to parse the assertions (but not necessarily analyze them yet). (The analyzer should parse asserts in initializer lists. #27142)
• the formatter to parse the assertions. (Formatter should handle asserts in initializer list. dart_style#522)

That should be sufficient for the people behind issue #24841 to test out the implementation and see if it covers their needs.