Fix FreeList::zapFreedMemory to fail "use-of-uninitialized-value" on MSAN

Source/platform/heap/Heap.h

Index: Source/platform/heap/Heap.h
diff --git a/Source/platform/heap/Heap.h b/Source/platform/heap/Heap.h
index 2100b6ef2ae2681c330e16c85606fe0d3231d0df..0a5cdbde6459496027a62956e27922a449e3e032 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -78,7 +78,12 @@ const uint8_t reuseForbiddenZapValue = 0x2c;
 // memory is zeroed out when the memory is reused in Heap::allocateObject().
 // In production builds, memory is not zapped (for performance). The memory
 // is just zeroed out when it is added to the free list.
-#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
+#if defined(MEMORY_SANITIZER)
+#define SET_MEMORY_INACCESSIBLE(address, size) \
+    FreeList::zapFreedMemory(address, size);

[Alexander Potapenko, 2015/07/29 13:39:42]

Please add a TODO here indicating that we actually do need MSan poisoning, but
it'll be added later.

[kojii, 2015/07/29 14:30:06]

Done.

+#define SET_MEMORY_ACCESSIBLE(address, size) \
+    memset((address), 0, (size))
+#elif ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
 #define SET_MEMORY_INACCESSIBLE(address, size) \
     FreeList::zapFreedMemory(address, size);   \
     ASAN_POISON_MEMORY_REGION(address, size)