Add an internal field to each wasm function to keep a reference to the module. (So the GC can do the right thing when you only hold references to wasm functions but not the module).

Use Realloc carefully, to avoid copying from out of bounds.

Make snprintf use platform independent.

Don't disconnect external arraybuffers provided for the heap.

R=ahaas@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1531243003

Cr-Commit-Position: refs/heads/master@{#32951}