debug: turn off sparse bitmap pointer alignment.

third_party/WebKit/Source/platform/heap/HeapPage.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 1484 matching lines @@
       compact->relocate(payload, compactFrontier + sizeof(HeapObjectHeader));
     }
     headerAddress += size;
     markedObjectSize += size;
     allocationPoint += size;
     DCHECK(allocationPoint <= currentPage->payloadSize());
   }
   if (markedObjectSize)
     pageArena->getThreadState()->increaseMarkedObjectSize(markedObjectSize);
 
+  Address unusedStart;
+  size_t unusedSize;
+  if (currentPage != this) {
+    unusedStart = payload();
+    unusedSize = payloadSize();
+  } else {
+    unusedStart = payload() + allocationPoint;
+    unusedSize = payloadSize() - allocationPoint;
+  }
 #if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER) || \
     defined(MEMORY_SANITIZER)
   // Zap the page, which is now available and will either be compacted into
   // or freed.
-  if (currentPage != this) {
-    FreeList::zapFreedMemory(payload(), payloadSize());
-  } else {
-    FreeList::zapFreedMemory(payload() + allocationPoint,
-                             payloadSize() - allocationPoint);
-  }
+  FreeList::zapFreedMemory(unusedStart, unusedSize);
+#else
+  memset(unusedStart, 0, unusedSize);
 #endif
 }
 
 void NormalPage::makeConsistentForGC() {
   size_t markedObjectSize = 0;
   for (Address headerAddress = payload(); headerAddress < payloadEnd();) {
     HeapObjectHeader* header =
         reinterpret_cast<HeapObjectHeader*>(headerAddress);
     ASSERT(header->size() < blinkPagePayloadSize());
     // Check if a free list entry first since we cannot call
@@ skipping 375 matching lines @@
 
   m_hasEntries = true;
   size_t index = hash(address);
   ASSERT(!(index & 1));
   Address cachePage = roundToBlinkPageStart(address);
   m_entries[index + 1] = m_entries[index];
   m_entries[index] = cachePage;
 }
 
 }  // namespace blink