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This changes PolicyCompiler to skip the pass that converts ResultExprs
into ErrorCodes, and instead it directly emits instructions using
CodeGen.

Reduces the size of sandbox_linux_unittests in release builds on amd64
by about 30kB.

BUG=414363

Review URL: https://codereview.chromium.org/1309963002

Cr-Commit-Position: refs/heads/master@{#347470}