Adds Android native API for creating VideoTrackSourceInterface objects
that can be fed frames using VideoCapturer.CapturerObserver.
NativeCapturerObserver is moved out of VideoSource because it will now
be used without a VideoSource. It now takes a pointer to
AndroidVideoTrackSource directly instead of VideoTrackSourceProxy.
VideoSource and NativeCapturerObserver JNI code is moved away from
androidvideotracksource.cc to their own files. This allows using
AndroidVideoTrackSource independently.
Bug: webrtc:8769
Change-Id: Ifb9e1eb27d4c8237597d19d932ca6e863abb4d27
Reviewed-on: https://webrtc-review.googlesource.com/76924
Reviewed-by: Paulina Hensman <phensman@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23269}
ff1de0af6b