Various ASan exemptions to allow Oilpan pre-sweep poisoning of unmarkeds.

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index 699866a4516830374b32646ac8351c86a8c97e33..1b20f981cf9b388edb60b2582881add495171f4b 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -895,10 +895,8 @@ void ThreadState::preSweep()
     }
 
 #if defined(ADDRESS_SANITIZER)
-// TODO(haraken): Currently we cannot enable the poisoning because we have
-// real bugs where destructors touch other on-heap objects. Remove all the bugs
-// and enable the poisoning.
-#if 0
+// TODO(Oilpan): enable the poisoning always.
+#if ENABLE(OILPAN)
     for (int i = 0; i < NumberOfHeaps; i++)
         m_heaps[i]->poisonUnmarkedObjects();
 #endif