This will be used to pass parameters of wasm functions to the wasm
interpreter. All of them need to be packed into one buffer, which is
then passed to the interpreter.

R=ahaas@chromium.org, titzer@chromium.org
BUG=v8:5822

Review-Url: https://codereview.chromium.org/2624183002
Cr-Commit-Position: refs/heads/master@{#42239}