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Expands testing in a few ways:
1. Adds an additional test file to fully parse.
2. Checks validity of parsed fields in SPS.
3. Adds a fuzzer (it even found a bug already).

BUG=chromium:1141237,b:153111783
TEST=media_unittests pass, fuzzer builds/runs

Change-Id: I3036c2e28466e460ba35647bea38fd53d491b844
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495344Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Cr-Commit-Position: refs/heads/master@{#820455}