PPB_VideoEncoder API review

[Bill Budge]

I've had requests from internal and external developers for PPB_VideoEncoder to be a Stable interface. This has been shipping in Chrome for a while as a Dev channel API. It's very similar in design to the Stable PPB_VideoDecoder API, and shares some supporting structs and enums.

Here's a link to the IDL:

https://code.google.com/p/chromium/codesearch#chromium/src/ppapi/api/ppb_video_encoder.idl&q=ppb_video_encoder.idl&sq=package:chromium&type=cs