User Activation v2 with parent-to-child postMessages

Test instruction: Never interact outside the green area: (a) Select a test API. (b) Click the button for desired postMessage sequence.

Expectation: Node of these buttons should be able to call the test API. User Activation v2 works in each case.

User-activation-gated API to test:

Each button below sends three messages:

requests in first message.

requests in second message.

requests in third message.