This runtime function in question can indirectly be fuzzed by the two
assertion methods "assertOptimized" and "assertUnoptimized" that our
test harness provides for the "mjsunit" test suite.

R=ishell@chromium.org
BUG=chromium:627841

Review-Url: https://codereview.chromium.org/2145993002
Cr-Commit-Position: refs/heads/master@{#37722}