Add support for Http.riskyRequest, Http.riskyTask

What is different between risky and non-risky requests that someone would want to assert about?

Start by reading the existing Http.riskyRequest and Http.riskyTask entry points and their related tests, then compare them with the non-risky request and task APIs. Determine which observable differences users need to assert and document the expected behavior before implementing support and tests.

Written by the indexing model from the issue text.