Add a CompareAndSwapUint32 variant to AtomicOperations so that it is possible to a CAS of a 32 bit …

runtime/vm/atomic.h

Index: runtime/vm/atomic.h
diff --git a/runtime/vm/atomic.h b/runtime/vm/atomic.h
index 9d1fd1375fa3bca49a9250cd0e9e9893b1fefc83..809548a3c38933453dc7c5d92db2d06076cbe89d 100644
--- a/runtime/vm/atomic.h
+++ b/runtime/vm/atomic.h
@@ -33,6 +33,8 @@ class AtomicOperations : public AllStatic {
   //
   // NOTE: OK to use with memory locations that are accessed by generated code
   static uword CompareAndSwapWord(uword* ptr, uword old_value, uword new_value);
+  static uint32_t CompareAndSwapUint32(
+      uint32_t* ptr, uint32_t old_value, uint32_t new_value);
 
   // Performs a load of a word from 'ptr', but without any guarantees about
   // memory order (i.e., no load barriers/fences).