GitLab

This started out as simply converting NaCl's baseline policy to bpf_dsl,
but that led me down the rabbit hole of converting a bunch of remaining
uses of SandboxBPFPolicy within content too.  There are still a few
lingering dependencies on sandbox_bpf.h after this CL, but not many.

BUG=414363

Review URL: https://codereview.chromium.org/570763002

Cr-Commit-Position: refs/heads/master@{#294871}