Fix pipeThrough error and track API changes

[aboba]

The current sample throws when attempting to send over a uni-directional stream.

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[jeffposnick]

R: @bashi and @yutakahirano

[google-cla[bot]]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[jeffposnick]

Thank you, @aboba & co.! If you could follow the CLA steps outlined in https://github.com/GoogleChrome/samples/pull/752#issuecomment-966188534 I'll get this merged.