Add unittest for I420Buffer::Rotate.
Add unittest for I420Buffer::Rotate.

Also change pointer to const ref for CheckCrop helper.

BUG=webrtc:5682

Review-Url: https://codereview.webrtc.org/2406463002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14663}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: f33970b15e0eeb46548fa602f6d0c1fcfd44dd19

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