08ab47dddf
@staticInterop members will start disallowing tear-offs, so this member should turn into a closure. Unblocks a roll in the SDK that disallows tear-offs. ## Pre-launch Checklist - [X] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [X] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [X] I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides]. - [X] I listed at least one issue that this PR fixes in the description above. - [X] I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See [testing the engine] for instructions on writing and running engine tests. - [X] I updated/added relevant documentation (doc comments with `///`). - [X] I signed the [CLA]. - [X] All existing and new tests are passing.