LayoutTests: Move internal GC functions to resources/gc.js

Bug: chromium:843903
Change-Id: I8509394ab507c0950b266c2e43f1484a67523af7
Reviewed-on: https://chromium-review.googlesource.com/1242465
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593888}
19 files changed