Implement debugQuickLookObject for RTCI420Buffers and RTCCVPixelBuffers.
Also draw gradients consistently regardless of endianness in the unit
tests for RTCCVPixelBuffers and ObjCVideoTrackSource.
Bug: webrtc:9007
Change-Id: Ia5a3d0905a763efc190165471983061fc07551f2
Reviewed-on: https://webrtc-review.googlesource.com/64987
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22746}