When WebAssembly.instantiate or WebAssembly.instantiateStreaming is
called in JavaScript, internally we transfrom it into
WebAssembly.compile(buffer).then(WebAssembly.instantiate). However,
modifying the prototype of WebAssembly.Module can change the result of
WebAssembly.compile(buffer). With this CL we make sure that even if the
result of WebAssembly.compile is modified, there is still no type
confusion. In the long term we have to do a refactoring and remove
this internal transformation.

R=mstarzinger@chromium.org

Bug: chromium:837417
Change-Id: I376068b8b8b01b991ec450162da6a62ae7030c62
Reviewed-on: https://chromium-review.googlesource.com/1032392
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52859}