In CreateModuleObjectFromBytes, pointers to the raw bytes will be stored
inside the decoded WasmModule, and still used after allocating V8 stuff
in WasmModule::CompileFunctions. We thus cannot pass a raw pointer to
the V8 heap.
Fix this by copying the bytes before decoding.

R=mtrofin@chromium.org, titzer@chromium.org

Review-Url: https://codereview.chromium.org/2402633002
Cr-Commit-Position: refs/heads/master@{#40077}