With this CL the AstDecoder produces an error if it encounters a
grow_memory instruction in an asmjs module. Additionally asmjs
instructions are not allowed anymore in wasm modules.

BUG=chromium:644674
R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2324733002
Cr-Commit-Position: refs/heads/master@{#39339}