Video frames are about to be shared between the decoder, the data
provider, the display sink, and Web painting code. Passing them by
value keeps ownership tied to the old bitmap-shaped pipeline and makes
later lifetime changes harder to reason about.
Make VideoFrame ref-counted and return NonnullRefPtr from the decoder
and media queues. This changes ownership only: a VideoFrame still wraps
an ImmutableBitmap at this point, so playback behavior remains
unchanged while later commits can move storage and painting
independently.
This saves us from having our own color conversion code, which was
taking up a fair amount of time in VideoDataProvider. With this change,
we should be able to play high resolution videos without interruptions
on machines where the CPU can keep up with decoding.
In order to make this change, ImmutableBitmap is now able to be
constructed with YUV data instead of an RBG bitmap. It holds onto a
YUVData instance that stores the buffers of image data, since Skia
itself doesn't take ownership of them.
In order to support greater than 8 bits of color depth, we normalize
the 10- or 12-bit color values into a 16-bit range.
