Make NoReloadScope thread safe

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 6973d8b42a03c14a8ead95c8ca2e7e1935166d9e..262a3284b909e1b5f6726dea50a8a97484d03b99 100644
--- a/runtime/vm/atomic_test.cc
+++ b/runtime/vm/atomic_test.cc
@@ -26,6 +26,22 @@ UNIT_TEST_CASE(FetchAndDecrement) {
 }
 
 
+UNIT_TEST_CASE(FetchAndIncrementSigned) {
+  intptr_t v = -42;
+  EXPECT_EQ(static_cast<intptr_t>(-42),
+            AtomicOperations::FetchAndIncrement(&v));
+  EXPECT_EQ(static_cast<intptr_t>(-41), v);
+}
+
+
+UNIT_TEST_CASE(FetchAndDecrementSigned) {
+  intptr_t v = -42;
+  EXPECT_EQ(static_cast<intptr_t>(-42),
+            AtomicOperations::FetchAndDecrement(&v));
+  EXPECT_EQ(static_cast<intptr_t>(-43), v);
+}
+
+
 UNIT_TEST_CASE(IncrementBy) {
   intptr_t v = 42;
   AtomicOperations::IncrementBy(&v, 100);