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
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