The term memory usually refers to the wasm memory. In the
{NativeModule}, we store pools for allocated and available code space.
This CL changes naming to make clear that this is code space and not
memory.

R=titzer@chromium.org

Bug: v8:7754
Change-Id: I195bf5c9227ad246af302ae1e98f9c839a02adbf
Reviewed-on: https://chromium-review.googlesource.com/1061495Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53208}