Rearranged types a bit

allocator_internal.h

@@ -20,9 +20,9 @@ typedef struct TreeAlloc {
   struct TreeAlloc *parent;
   struct TreeAlloc *left;
   struct TreeAlloc *right;
+  uintptr_t size;
   struct TreeAlloc *before;
   struct TreeAlloc *after;
-  uintptr_t size;
 } TreeAlloc;
 
 typedef struct FreeSpace {
@@ -30,8 +30,6 @@ typedef struct FreeSpace {
   struct FreeSpace *parent;
   struct FreeSpace *left;
   struct FreeSpace *right;
-  struct TreeAlloc *before;
-  struct TreeAlloc *after;
   uintptr_t size;
 } FreeSpace;
 
@@ -40,9 +38,9 @@ typedef struct WatermarkAlloc {
   struct TreeAlloc *parent;
   struct TreeAlloc *left;
   struct TreeAlloc *right;
+  uintptr_t size;
   struct TreeAlloc *before;
   struct TreeAlloc *after;
-  uintptr_t size;
   int num_allocs;
   void *next_alloc;
 } WatermarkAlloc;