Fix race in GC sweeper and isolate reload rollback.

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index f81e39a72c27e346e885b3b1222602aff7c6613b..12dd5fa2f6fdcc37fd861a2de0c6adc4eb08164f 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -555,7 +555,7 @@ class Isolate : public BaseIsolate {
   // True during top level parsing.
   bool IsTopLevelParsing() {
     const intptr_t value =
-        AtomicOperations::LoadRelaxedIntPtr(&top_level_parsing_count_);
+        AtomicOperations::LoadRelaxed(&top_level_parsing_count_);
     ASSERT(value >= 0);
     return value > 0;
   }
@@ -576,7 +576,7 @@ class Isolate : public BaseIsolate {
     }
   }
   intptr_t loading_invalidation_gen() {
-    return AtomicOperations::LoadRelaxedIntPtr(&loading_invalidation_gen_);
+    return AtomicOperations::LoadRelaxed(&loading_invalidation_gen_);
   }
 
   // Used by background compiler which field became boxed and must trigger