debug: turn off sparse bitmap pointer alignment.

third_party/WebKit/Source/platform/heap/HeapPage.cpp

Index: third_party/WebKit/Source/platform/heap/HeapPage.cpp
diff --git a/third_party/WebKit/Source/platform/heap/HeapPage.cpp b/third_party/WebKit/Source/platform/heap/HeapPage.cpp
index 8dc5d2d0155f2c76ae5d63252c4a9b1b2475f910..99733a57641124d5ff50ad005342f48da5e1fdbd 100644
--- a/third_party/WebKit/Source/platform/heap/HeapPage.cpp
+++ b/third_party/WebKit/Source/platform/heap/HeapPage.cpp
@@ -1502,16 +1502,22 @@ void NormalPage::sweepAndCompact(CompactionContext& context) {
   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
 }