There's no need to mark these as possibly-direct-eval, since all such an
eval-tagged string will ever get passed is the array of string parts, which
will be immediately returns (since it's not a string). It will
never do a lookup in the current scope, nor (in sloppy mode) introduce
new declarations.

This patch is not intended to change behavior, but I've added tests that
demonstrate the stuff explained in the preceding paragraph.

Review URL: https://codereview.chromium.org/1580463003

Cr-Commit-Position: refs/heads/master@{#33245}