DefaultExtractorInput.SCRATCH_SPACE buffer is used to skip data by
reading it into this buffer and discarding.
Simultaneous use of skip methods corrupts this buffer. Normally the
read data is discarded so it doesn't matter but the underlying
DataSource may use the buffer too. If it's a CacheDataSource it uses
this buffer to read data from upstream then write to cache.
Issue: #3762
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=184502170
