According to the spec, if an imported function gets exported, the
exported function has to be identical to to imported function.

With this CL we initialize the list of potential js_wrappers_ with all
wasm function we imported. Therefore no new wrappers are generated for
these functions.

R=clemensh@chromium.org

Bug: v8:7364
Change-Id: Ibcd47d8fcc4c2fb5740d57ea547fbd01c2a4e80a
Reviewed-on: https://chromium-review.googlesource.com/901626
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51244}