Shuffle fields to make simarm and arm agree on the offset of Heap::new_space_.to_.

runtime/vm/heap.h

Index: runtime/vm/heap.h
diff --git a/runtime/vm/heap.h b/runtime/vm/heap.h
index 287cbdca14242cbe353792ed7a02897539f0b122..1526424a91cccf1a3b5c5f07a55607caa1a0d3ac 100644
--- a/runtime/vm/heap.h
+++ b/runtime/vm/heap.h
@@ -340,16 +340,17 @@ class Heap {
   void GetMergedAddressRange(uword* start, uword* end) const;
 
   Isolate* isolate_;
-  Monitor* barrier_;
-  Monitor* barrier_done_;
 
   // The different spaces used for allocation.
-  Scavenger new_space_;
+  ALIGN8 Scavenger new_space_;
   PageSpace old_space_;
 
   WeakTable* new_weak_tables_[kNumWeakSelectors];
   WeakTable* old_weak_tables_[kNumWeakSelectors];
 
+  Monitor* barrier_;
+  Monitor* barrier_done_;
+
   // GC stats collection.
   GCStats stats_;