Add partitionAllocActualSize() for predicting actual size of allocation

Source/wtf/PartitionAlloc.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 508 matching lines @@
             page->nextPage = 0;
         }
     }
 
     bucket->activePagesHead = 0;
     return false;
 }
 
 static ALWAYS_INLINE void* partitionDirectMap(PartitionRootBase* root, int flags, size_t size)
 {
-    size += kSystemPageOffsetMask;
-    size &= kSystemPageBaseMask;
+    size = partitionDirectMapSize(size);
+
     // Because we need to fake looking like a super page, We need to allocate
     // a bunch of system pages more than "size":
     // - The first few system pages are the partition page in which the super
     // page metadata is stored. We fault just one system page out of a partition
     // page sized clump.
     // - We add a trailing guard page.
     size_t mapSize = size + kPartitionPageSize + kSystemPageSize;
     // Round up to the allocation granularity.
     mapSize += kPageAllocationGranularityOffsetMask;
     mapSize &= kPageAllocationGranularityBaseMask;
@@ skipping 314 matching lines @@
     printf("total live: %zu bytes\n", totalLive);
     printf("total resident: %zu bytes\n", totalResident);
     printf("total freeable: %zu bytes\n", totalFreeable);
     fflush(stdout);
 }
 
 #endif // !NDEBUG
 
 } // namespace WTF