Oilpan: Use gcInfoIndexForFreeListHeader in HeapObjectHeader's constructor
Oilpan: Use gcInfoIndexForFreeListHeader in HeapObjectHeader's constructor

Very simple code clean-up.

BUG=

Review URL: https://codereview.chromium.org/1382133002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#352286}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk