GitLab

Allow the library to process 8 bit (plus high bitdepth internal), 10
bit, and 12 bit files.

Only for x86 targets. Performance for 8 bit (regular internal) is within
1-2% for these targets.

BUG=445071
R=jzern

Review-Url: https://codereview.chromium.org/2361263002
Cr-Commit-Position: refs/heads/master@{#420523}