Delete webrtc::VideoFrame methods buffer and stride.

To make the HasOneRef/IsMutable hack work, also had to change the
video_frame_buffer method to return a const ref to a scoped_ref_ptr,
to not imply an AddRef.

BUG=webrtc:5682

Review-Url: https://codereview.webrtc.org/1900673002
Cr-Original-Commit-Position: refs/heads/master@{#12557}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a0591b54730c097b2a1236b3343d258e397ed018
26 files changed