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

Source/platform/heap/Heap.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 60 matching lines @@
 // list in the next addToFreeList().
 const uint8_t reuseAllowedZapValue = 0x2a;
 // A zap value used for freed memory that is forbidden to be added to the free
 // list in the next addToFreeList().
 const uint8_t reuseForbiddenZapValue = 0x2c;
 
 // In non-production builds, memory is zapped when it's freed. The zapped
 // 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)
+// TODO(kojii): We actually need __msan_poison/unpoison here, but it'll be
+// added later.
+#define SET_MEMORY_INACCESSIBLE(address, size) \
+    FreeList::zapFreedMemory(address, size);
+#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)
 #define SET_MEMORY_ACCESSIBLE(address, size) \
     ASAN_UNPOISON_MEMORY_REGION(address, size);    \
     memset((address), 0, (size))
 #else
 #define SET_MEMORY_INACCESSIBLE(address, size) memset((address), 0, (size))
 #define SET_MEMORY_ACCESSIBLE(address, size) do { } while (false)
 #endif
@@ skipping 1296 matching lines @@
     size_t copySize = previousHeader->payloadSize();
     if (copySize > size)
         copySize = size;
     memcpy(address, previous, copySize);
     return address;
 }
 
 } // namespace blink
 
 #endif // Heap_h