Reland "Promise.race() based select like pipeTo implementation"
Update acknowledgments.
Add [[started]] to WritableStream IDL
Basic transform stream
Got default close propagation working
Implement flushing
Handle errors thrown by transform
Fix tests in light of bda8ab
Initial draft.

This crashes if I set underlyingSourceRate to 2!
Add strategies to transform streams.

No tests, eek, I am a bad person! Don't let this get in master!
Add a transform in the middle, and some comments
Fancy, exhaustive, and fairly useless test runner.

The output is not something you can make decisions on. We need aggregate data and a way of comparing between runs, and something you can watch as it runs. And it's probably still too slow.
Make the output more useful.

Now it scrolls by one line per test.