This is some initial cleanup to keep /src clean. The
AccountingAllocator is actually exclusively used by zones and this
common subfolder makes that more clear.

BUG=v8:5409

Review-Url: https://codereview.chromium.org/2344143003
Cr-Commit-Position: refs/heads/master@{#39558}

It can now deal with multiple objects at the same time (but no
aliasing), and it propagates store information upwards across effect
chain splits.

R=jarin
BUG=

Review-Url: https://codereview.chromium.org/2159303002
Cr-Commit-Position: refs/heads/master@{#38509}

R=jarin@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2087483003
Cr-Commit-Position: refs/heads/master@{#37220}