For the wasm2js wrappers we have an optimization to call a JavaScript
function directly if the signature of the JavaScript function matches
the signature of the WebAssembly import. However, we are not supposed
to do this optimization if the imported function is a constructor,
because constructors can only be called with `new`. With this CL we
do not apply this optimization when the imported function is a
constructor.

R=titzer@chromium.org

Bug: chromium:824859
Change-Id: I1722367bd865d0b129eadf7d4849182410447179
Reviewed-on: https://chromium-review.googlesource.com/985974Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52296}