This CL introduces two tests to verify that the correct memory is
accessed when a wasm module invokes an wasm function imported from a
second module that accesses its (i.e., second module's) memory.

The first test verifies that the second module's memory is accessed in
case the first module does not have memory. In the second test, both the
modules have memory.

R=ahaas@chromium.org,clemensh@chromium.org,gdeepti@chromium.org

Change-Id: I75c3a5335583a91af0e7e4179c482142165b1c01
Reviewed-on: https://chromium-review.googlesource.com/637837
Commit-Queue: Enrico Bacis <enricobacis@google.com>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47702}