Fix tests regress-336820 and regress-678917.

test/mjsunit/regress/regress-678917.js

Index: test/mjsunit/regress/regress-678917.js
diff --git a/test/mjsunit/regress/regress-678917.js b/test/mjsunit/regress/regress-678917.js
index accb5156238600e524deed7808c1e4440d064efc..cb88ead5ba9f8c772ab377710840b2bec1df9e89 100644
--- a/test/mjsunit/regress/regress-678917.js
+++ b/test/mjsunit/regress/regress-678917.js
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// Flags: --max-old-space-size=400
+
 s1 = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';
 s1 += s1;
 s1 += s1;