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- don't clear the error callback prior to calling it
- implement encodeQueueSize to signal backpressure
- add extra error logging for VpxVideoEncoder
- disable vp9 profiles 1 and 3 (not yet implemented)

And opportunistically mark a number of inputs
in IDL as required
- timestamp (its required for creation of VideoFrame internally)
- error and output callbacks (duh).

Remove ? from duration input dictionary. Its not required,
no need to null.

Bug: 1094166, 1116617

Change-Id: I9577bc42d1f24c2ec14885401e87337ba0937e43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2355276
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798473}