Fix GC Mole warning

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 72b8524c08340d4ab6436a45fd76733752ac9340..41f9d0d5ccdecae37ed1cf08206f09136a6f8476 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -3230,8 +3230,9 @@ class HConstant: public HTemplateInstruction<0> {
   }
 
   bool InstanceOf(Handle<Map> map) {
-    return handle()->IsJSObject() &&
-        Handle<JSObject>::cast(handle())->map() == *map;
+    Handle<Object> constant_object = handle();
+    return constant_object->IsJSObject() &&
+        Handle<JSObject>::cast(constant_object)->map() == *map;
   }
 
   bool IsSpecialDouble() const {