Make assertion scopes thread safe.

src/api.h

Index: src/api.h
diff --git a/src/api.h b/src/api.h
index 62380ce651249d86548c37679c9b2deb248c1bfd..3d7e3778e69265b8066de0f8cbaf0edb31a50b1d 100644
--- a/src/api.h
+++ b/src/api.h
@@ -636,7 +636,7 @@ void HandleScopeImplementer::DeleteExtensions(internal::Object** prev_limit) {
     internal::Object** block_start = blocks_.last();
     internal::Object** block_limit = block_start + kHandleBlockSize;
 #ifdef DEBUG
-    // NoHandleAllocation may make the prev_limit to point inside the block.
+    // SealHandleScope may make the prev_limit to point inside the block.
     if (block_start <= prev_limit && prev_limit <= block_limit) {
 #ifdef ENABLE_EXTRA_CHECKS
       internal::HandleScope::ZapRange(prev_limit, block_limit);