PartitionAlloc: Make in-place realloc() less likely to happen

Source/wtf/PartitionAlloc.h

Index: Source/wtf/PartitionAlloc.h
diff --git a/Source/wtf/PartitionAlloc.h b/Source/wtf/PartitionAlloc.h
index 66c7369c221e5f76051c6b02911f9b1d90cddaba..78abbabf47c2deeb2bfc393bdd0e798b93d88471 100644
--- a/Source/wtf/PartitionAlloc.h
+++ b/Source/wtf/PartitionAlloc.h
@@ -183,7 +183,7 @@ static const size_t kGenericNumBucketsPerOrder = 1 << kGenericNumBucketsPerOrder
 static const size_t kGenericSmallestBucket = 1 << (kGenericMinBucketedOrder - 1);
 static const size_t kGenericMaxBucketSpacing = 1 << ((kGenericMaxBucketedOrder - 1) - kGenericNumBucketsPerOrderBits);
 static const size_t kGenericMaxBucketed = (1 << (kGenericMaxBucketedOrder - 1)) + ((kGenericNumBucketsPerOrder - 1) * kGenericMaxBucketSpacing);
-static const size_t kGenericMinDirectMappedDownsize = 16 * kPartitionPageSize; // Limit when downsizing a direct mapping using realloc().
+static const size_t kGenericMinDirectMappedDownsize = kGenericMaxBucketed + 1; // Limit when downsizing a direct mapping using realloc().
 static const size_t kGenericMaxDirectMapped = INT_MAX - kSystemPageSize;
 static const size_t kBitsPerSizet = sizeof(void*) * CHAR_BIT;