Add missing case for TextInput.requestAutofill

[LongCatIsLooong]

I'm not sure how I can write a test for this change, everything in the call path seems to be private.

[justinmc]

LGTM 👍

Maybe Gary will have an idea about testing. At least it's covered by tests in the framework if it's not possible.

[LongCatIsLooong]

Hi @GaryQian what would be a test to add for this PR?

[GaryQian]

You may be able to extend DartExecutor to log the messages it receives, and then check that a TextInputChannel constructed with this TestDartExecutor is getting sent the right success messages when requestAutofill is called. I don't think this line of testing currently exists though, so you may have to write it. Just a thought from looking at code, have not verified this way would work, though it looks like it should.

[LongCatIsLooong]

@GaryQian is there a way to send a message to a BinaryMessenger? I wanted to send a "TextInput.requestAutofill" message to the TextInputChannel and verify requestAutofill gets called, but couldn't find a way to.