Track based on JSArrayBuffer addresses instead of the attached backing store.
This way we can later on iterate buffers on a single page.

BUG=chromium:581412
LOG=N
R=jochen@chromium.org, hpayer@chromium.org

Review-Url: https://codereview.chromium.org/1936233002
Cr-Commit-Position: refs/heads/master@{#36140}