Reject vp8 video having alpha and image planes of different sizes.
Previously we would accept malformed vp8 video files that had alpha and
image planes with different dimensions. Now they result in a decode error.
Also use the alpha image stride when copying the alpha plane, because it
technically doesn't have to be the same as the image stride.
BUG=449958
TEST=ffmpeg_regression_tests
Review URL: https://codereview.chromium.org/858303002
Cr-Commit-Position: refs/heads/master@{#312420}
2 files changed
