Fix flag convention in handle count tests and comment.

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 2df5d040b6577965b19b6e1e2b6acfbe86cf25c0..eb2023cf335d8cc93571d857e6268108b0e081a2 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -226,7 +226,7 @@ class HandleScope {
 
   Isolate* isolate() { return isolate_; }
 
-  // Limit for number of handles with --check_handle-count. This is
+  // Limit for number of handles with --check-handle-count. This is
   // large enough to compile natives and pass unit tests with some
   // slack for future changes to natives.
   static const int kCheckHandleThreshold = 30 * 1024;