Fix NoTrackDoubleFieldsForSerializerScope.

BUG=v8:3143
LOG=N
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/144473005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19226 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/bootstrapper.cc

@@ -2566,7 +2566,9 @@ class NoTrackDoubleFieldsForSerializerScope {
     }
   }
   ~NoTrackDoubleFieldsForSerializerScope() {
-    FLAG_track_double_fields = flag_;
+    if (Serializer::enabled()) {
+      FLAG_track_double_fields = flag_;
+    }
   }
 
  private: