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

runtime/vm/atomic_test.cc

Index: runtime/vm/atomic_test.cc
diff --git a/runtime/vm/atomic_test.cc b/runtime/vm/atomic_test.cc
index 5e22606047e83c6b6bb253fce715d332352ccabd..e7e366641f92332e5fdba0e282614a75af891ece 100644
--- a/runtime/vm/atomic_test.cc
+++ b/runtime/vm/atomic_test.cc
@@ -31,4 +31,22 @@ UNIT_TEST_CASE(LoadRelaxed) {
   EXPECT_EQ(static_cast<uword>(42), AtomicOperations::LoadRelaxed(&v));
 }
 
+
+UNIT_TEST_CASE(CompareAndSwapWord) {
+  uword old_value = 42;
+  uword new_value = 100;
+  uword result = AtomicOperations::CompareAndSwapWord(
+      &old_value, old_value, new_value);
+  EXPECT_EQ(static_cast<uword>(42), result);
+}
+
+
+UNIT_TEST_CASE(CompareAndSwapUint32) {
+  uint32_t old_value = 42;
+  uint32_t new_value = 100;
+  uint32_t result = AtomicOperations::CompareAndSwapUint32(
+      &old_value, old_value, new_value);
+  EXPECT_EQ(static_cast<uint32_t>(42), result);
+}
+
 }  // namespace dart