The `setCompositionRecording` API on nsIDOMWindowUtils has been broken up into
two new APIs:

* `startCompositionRecording()`, which starts the composition recorder; and
* `stopCompositionRecording(bool writeToDisk)` which stops the composition
  recorder and either returns a Promise that resolves to the collected frames
  or returns a Promise that resolves when the frames have been written to disk.

The collected frames are serialized over IPC as part of a Shmem as to not
approach the IPC data transfer limit.

Differential Revision: https://phabricator.services.mozilla.com/D47818

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extra : moz-landing-system : lando