Change signature of atomic increment/decrement functions to return void.

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 db9be229f76252105474269783cd0aa7ca824b12..6973d8b42a03c14a8ead95c8ca2e7e1935166d9e 100644
--- a/runtime/vm/atomic_test.cc
+++ b/runtime/vm/atomic_test.cc
@@ -26,18 +26,16 @@ UNIT_TEST_CASE(FetchAndDecrement) {
 }
 
 
-UNIT_TEST_CASE(FetchAndIncrementBy) {
+UNIT_TEST_CASE(IncrementBy) {
   intptr_t v = 42;
-  EXPECT_EQ(static_cast<uintptr_t>(42),
-            AtomicOperations::FetchAndIncrementBy(&v, 100));
+  AtomicOperations::IncrementBy(&v, 100);
   EXPECT_EQ(static_cast<intptr_t>(142), v);
 }
 
 
-UNIT_TEST_CASE(FetchAndDecrementBy) {
+UNIT_TEST_CASE(DecrementBy) {
   intptr_t v = 42;
-  EXPECT_EQ(static_cast<uintptr_t>(42),
-            AtomicOperations::FetchAndDecrementBy(&v, 41));
+  AtomicOperations::DecrementBy(&v, 41);
   EXPECT_EQ(static_cast<intptr_t>(1), v);
 }