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

runtime/vm/atomic_linux.h

Index: runtime/vm/atomic_linux.h
diff --git a/runtime/vm/atomic_linux.h b/runtime/vm/atomic_linux.h
index dc57f2d7a1eeda2040ca4843ad2d510ebffe7140..1150857c1b79685545578e5c7d27f32a424f17d9 100644
--- a/runtime/vm/atomic_linux.h
+++ b/runtime/vm/atomic_linux.h
@@ -32,6 +32,13 @@ inline uword AtomicOperations::CompareAndSwapWord(uword* ptr,
                                                   uword new_value) {
   return __sync_val_compare_and_swap(ptr, old_value, new_value);
 }
+
+
+inline uint32_t AtomicOperations::CompareAndSwapUint32(uint32_t* ptr,
+                                                       uint32_t old_value,
+                                                       uint32_t new_value) {
+  return __sync_val_compare_and_swap(ptr, old_value, new_value);
+}
 #endif  // !defined(USING_SIMULATOR)
 
 }  // namespace dart