Oilpan: Do not add non-free headers to free list in ThreadHeap::assertEmpty.
Oilpan: Do not add non-free headers to free list in ThreadHeap::assertEmpty.

It is possible that a thread is involved to GC after ThreadHeap::
assertEmpty before ThreadState destruction.

BUG=388267
R=ager@chromium.org, haraken@chromium.org

Review URL: https://codereview.chromium.org/372213002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@177723 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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