PartitionAlloc: support in-place resize of directly mapped allocation

Source/wtf/PartitionAlloc.h

Index: Source/wtf/PartitionAlloc.h
diff --git a/Source/wtf/PartitionAlloc.h b/Source/wtf/PartitionAlloc.h
index 78e039f04cf5a5a97ef2bc1884a8d2d4aa3e7b5b..7dfc37a59b554767ac24da81e8bb5be09afa7053 100644
--- a/Source/wtf/PartitionAlloc.h
+++ b/Source/wtf/PartitionAlloc.h
@@ -571,6 +571,12 @@ ALWAYS_INLINE bool partitionBucketIsDirectMapped(PartitionBucket* bucket)
     return !bucket->numSystemPagesPerSlotSpan;
 }
 
+ALWAYS_INLINE bool partitionSizeIsDirectMapped(size_t size)

[Chris Evans, 2014/03/05 07:57:04]

I think we can make this private by moving to the .cpp (see comment in test
file).

+{
+    size = partitionCookieSizeAdjustAdd(size);
+    return size > kGenericMaxBucketed && size <= kGenericMaxDirectMapped;

[Chris Evans, 2014/03/05 07:57:04]

I think the second condition is a bit subtle here. I think I prefer a direct
RELEASE_ASSERT() check against newSize in realloc itself?

+}
+
 ALWAYS_INLINE size_t partitionDirectMapSize(size_t size)
 {
     // Caller must check that the size is not above the kGenericMaxDirectMapped