Add reftests that test the ImageRendering property on video (NativeTexture external images), JS-based ImageRendering changes and inequality of results between different ImageRendering settings. Also include a simple h264 mp4 with minimal lossy encoding. OSX fuzzing values determined by try run.
reftest is disabled on windows due to localized try readback errors that can't be reproduced.
MozReview-Commit-ID: 379PZsRE5d6
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extra : rebase_source : b990572c0f33860998eb5485824e417387d3e204