The WasmRunner now always holds a TestingModule, and allows to add
several functions to it. The prepares a change to always run wasm code
with a full module behind it, removing the special handling for "no wasm
instance" at runtime (http://crrev.com/2551053002).
This CL here also templatizes the WasmRunner such that the Call method must
be called with the same signature specified for the WasmRunner. This
already catched several mismatches there.

R=titzer@chromium.org, ahaas@chromium.org
BUG=v8:5620

Review-Url: https://codereview.chromium.org/2551043002
Cr-Commit-Position: refs/heads/master@{#41728}