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

Source/platform/heap/Heap.cpp

 /*
  * 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 1150 matching lines @@
     // region to the free list and reuse it for another object.
 #endif
     ASAN_POISON_MEMORY_REGION(address, size);
 
     int index = bucketIndexForSize(size);
     entry->link(&m_freeLists[index]);
     if (index > m_biggestFreeListIndex)
         m_biggestFreeListIndex = index;
 }
 
-#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
+#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER)
 NO_SANITIZE_ADDRESS
+NO_SANITIZE_MEMORY
 void NEVER_INLINE FreeList::zapFreedMemory(Address address, size_t size)
 {
     for (size_t i = 0; i < size; i++) {
         // See the comment in addToFreeList().

[Alexander Potapenko, 2015/07/27 09:45:00]

NO_SANITIZE_MEMORY will remove checks for uninitialized reads in line 1178, so
there'll be no MSan reports in zapFreeMemory().
It will however preserve the code that marks address[i] as initialized in line
1179, so that random reads of that memory after it has been freed will not be
detected. Is that really what you want?

         if (address[i] != reuseAllowedZapValue)
             address[i] = reuseForbiddenZapValue;
     }
 }
 #endif
 
 void FreeList::clear()
 {
     m_biggestFreeListIndex = 0;
     for (size_t i = 0; i < blinkPageSizeLog2; ++i)
@@ skipping 1338 matching lines @@
 size_t Heap::s_allocatedObjectSize = 0;
 size_t Heap::s_markedObjectSize = 0;
 size_t Heap::s_persistentCount = 0;
 size_t Heap::s_persistentCountAtLastGC = 0;
 size_t Heap::s_collectedPersistentCount = 0;
 size_t Heap::s_partitionAllocSizeAtLastGC = 0;
 size_t Heap::s_heapSizePerPersistent = 0;
 double Heap::s_estimatedMarkingTimePerByte = 0.0;
 
 } // namespace blink