Rename to better capture what the files contain.

Removed includes of wasm-code-manager.h from .h files to improve
build time.

Bug: 
Change-Id: I0f0108cfb00b061c4433b6ff9670e9c4cae9c699
Reviewed-on: https://chromium-review.googlesource.com/807368Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49875}