I wrote these patches while trying to fix bug 1507952. The real fix turns out to be elsewhere, but they're good patches.

This also renames TeeState::promise to cancelPromise.

This also renames a few local variables to follow the `unwrapped` convention (arguments and locals that are not same-compartment with cx have names that start with `unwrapped`, unless they're wrapped or AutoRealm'd on the next line). Depends on D12349

This adds a missing "return undefined", but nothing downstream pays attention to the return value, so the bug was not observable from script. Depends on D12350

Depends on D12351

Pushed by jorendorff@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/2ed75fc212f1 Part 1: Update step numbers in ReadableStreamTee_Cancel. r=arai https://hg.mozilla.org/integration/autoland/rev/0038d6eebaef Part 2: Update step numbers in TeeReaderReadHandler and ReadableStreamTee_Pull. r=arai https://hg.mozilla.org/integration/autoland/rev/6552cbff38d2 Part 3: Update step numbers in TeeReaderClosedHandler. r=arai https://hg.mozilla.org/integration/autoland/rev/db9e52e671fc Part 4: Update step numbers in ReadableStreamTee. Comments only. r=arai

https://hg.mozilla.org/mozilla-central/rev/2ed75fc212f1 https://hg.mozilla.org/mozilla-central/rev/0038d6eebaef https://hg.mozilla.org/mozilla-central/rev/6552cbff38d2 https://hg.mozilla.org/mozilla-central/rev/db9e52e671fc

https://hg.mozilla.org/mozilla-central/rev/2ed75fc212f1 https://hg.mozilla.org/mozilla-central/rev/0038d6eebaef https://hg.mozilla.org/mozilla-central/rev/6552cbff38d2 https://hg.mozilla.org/mozilla-central/rev/db9e52e671fc